A bulk acoustic wave filter with improved membrane adhesion and its fabrication method

Abstract

This application discloses a bulk acoustic wave (BAW) filter with improved film-layer adhesion and its fabrication method. It relates to the field of filtering technology. The BAW filter includes a substrate and a resonant structure, wherein the resonant structure is disposed on the substrate and includes a working region and a non-working region surrounding the working region. In the non-working region, a buffer structure is provided between the piezoelectric layer of the resonant structure and adjacent film layers. By introducing a buffer structure in the non-working region, the stress distribution between the piezoelectric layer and adjacent film layers is made more uniform, reducing the stress difference between the piezoelectric layer and adjacent film layers. This effectively prevents separation of the piezoelectric layer and adjacent film layers or wafer warping, thereby enhancing the robustness and reliability of the device. This solves the technical problem in the prior art where the stress difference between the piezoelectric layer and adjacent film layers in BAW filters leads to device structural damage and reduced reliability.

Description

Technical Field

[0001] This application relates to the field of filtering technology, and in particular to a bulk acoustic wave filter that improves the adhesion of membrane layers and its manufacturing method. Background Technology

[0002] In the field of wireless communication technology, SAW filters and BAW filters are two crucial components, each playing a key role in different application scenarios.

[0003] BAW filters, or bulk acoustic wave filters, are based on bulk acoustic wave technology. When an alternating electric field is applied to both ends of a piezoelectric material, the material vibrates mechanically, and this vibration propagates within the material as bulk acoustic waves. By cleverly designing the structure and dimensions of the bulk acoustic wave filter, specific frequencies of bulk acoustic waves can propagate smoothly within the filter while suppressing other frequencies, thus achieving the filtering function.

[0004] D-BAW filters, or double-sided patterned bulk acoustic wave filters, are fabricated using a double-sided bonding process. Specifically, during fabrication, several fabrication steps are first performed on the front side of the wafer, and then the wafer is flipped over using bonding to perform subsequent fabrication steps. During packaging, the wafer is flipped again using bonding to perform several fabrication steps on the back side, thus achieving a double-sided process.

[0005] Bulk acoustic wave (BAW) filters consist of multiple thin films bonded together. However, due to differences in material properties, thermal expansion coefficients, lattice constant mismatches, film thickness variations, and defects and impurities between the piezoelectric layer and adjacent films, a stress difference exists between the piezoelectric layer and adjacent films. This stress difference can lead to separation between the piezoelectric layer and adjacent films or wafer warping, resulting in structural damage to the BAW filter and reduced reliability.

[0006] Regarding the technical problem of device structure damage and reduced reliability in the existing bulk acoustic wave filter due to the stress difference between the piezoelectric layer and the adjacent thin film, no effective solution has yet been proposed. Summary of the Invention

[0007] The embodiments of this disclosure provide a bulk acoustic wave filter with improved film-layer adhesion and a method for fabricating the same. This addresses at least the problem in the prior art where the stress difference between the piezoelectric layer and adjacent thin films in bulk acoustic wave filters leads to risks of device structural damage and reduced reliability.

[0008] According to one aspect of the present disclosure, a bulk acoustic wave filter with improved film adhesion is provided, comprising: a substrate and a resonant structure, wherein the resonant structure is disposed on the substrate, and the resonant structure includes a working region and a non-working region surrounding the working region, wherein a piezoelectric layer of the resonant structure has a buffer structure between it and an adjacent film layer in the non-working region.

[0009] Optionally, the resonant structure includes a first electrode, a second electrode, and a fence layer, wherein the first electrode is disposed on the side of the piezoelectric layer near the substrate and exposes at least a portion of the surface of the piezoelectric layer, and a first buffer structure is provided between the first electrode and the piezoelectric layer in the non-working region; the second electrode is disposed on the side of the piezoelectric layer away from the substrate; and the fence layer is disposed between the first electrode and the substrate, and covers a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer, and a second buffer structure is provided between the piezoelectric layer and the fence layer in the non-working region.

[0010] Optionally, in the non-working area, the surface of the first electrode near the substrate has a raised structure, and the fence layer covers the raised structure and a portion of the flat surface of the first electrode near the substrate.

[0011] Optionally, the bulk acoustic wave filter further includes a first protective structure and a second protective structure; wherein the first protective structure is disposed on the surface of the first electrode near the substrate and covers the protrusion structure; and the second protective structure is disposed on the exposed surface of the piezoelectric layer near the substrate and covers the second buffer structure.

[0012] Optionally, the resonant structure includes a first electrode, a second electrode, and a barrier layer, wherein the first electrode is disposed on the side of the piezoelectric layer near the substrate and exposes at least a portion of the surface of the piezoelectric layer; the second electrode is disposed on the side of the piezoelectric layer away from the substrate; and the barrier layer is disposed between the first electrode and the substrate, covering a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer, wherein a second buffer structure is provided between the piezoelectric layer and the barrier layer in the non-working area, and a third buffer structure is provided between the first electrode and the barrier layer.

[0013] Optionally, the resonant structure includes a first electrode, a second electrode, and a fence layer, wherein the first electrode is disposed on the side of the piezoelectric layer near the substrate and exposes at least a portion of the surface of the piezoelectric layer, and a first buffer structure is provided between the first electrode and the piezoelectric layer in the non-working region; the second electrode is disposed on the side of the piezoelectric layer away from the substrate; and the fence layer is disposed between the first electrode and the substrate, and covers a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer, a second buffer structure is provided between the piezoelectric layer and the fence layer in the non-working region, and a third buffer structure is provided between the first electrode and the fence layer.

[0014] Optionally, the resonant structure further includes a first protective structure and a second protective structure; wherein the first protective structure is disposed on the side surface of the first electrode near the substrate and covers the third buffer structure; and the second protective structure is disposed on the exposed surface of the piezoelectric layer near the substrate and covers the second buffer structure.

[0015] Optionally, the material of the buffer structure is phosphosilicate glass, undoped silicate glass, or borosilicate glass.

[0016] Optionally, the thickness of the buffer structure is 50-500 nm.

[0017] According to another aspect of the present disclosure, a method for fabricating a bulk acoustic wave filter with improved film adhesion is also provided, comprising: fabricating a substrate and a resonant structure, wherein the resonant structure is disposed on the substrate, and the resonant structure includes a working region and a non-working region surrounding the working region, wherein a buffer structure is provided between a piezoelectric layer of the resonant structure and an adjacent film layer in the non-working region.

[0018] Optionally, the process of fabricating the resonant structure includes: fabricating a first electrode, a second electrode, and a fence layer, wherein the first electrode is disposed on the side of the piezoelectric layer near the substrate and exposes at least a portion of the surface of the piezoelectric layer; a first buffer structure is provided between the first electrode and the piezoelectric layer in the non-working region; the second electrode is disposed on the side of the piezoelectric layer away from the substrate; and the fence layer is disposed between the first electrode and the substrate, covering a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer; a second buffer structure is provided between the piezoelectric layer and the fence layer in the non-working region; a protruding structure is provided on the surface of the first electrode near the substrate in the non-working region, and the fence layer covers the protruding structure and a portion of the flat surface of the first electrode near the substrate; and the fabrication method further includes: fabricating a first protective structure and a second protective structure; wherein the first protective structure is disposed on the surface of the first electrode near the substrate and covers the protruding structure; and the second protective structure is disposed on the exposed surface of the piezoelectric layer near the substrate and covers the second buffer structure.

[0019] Optionally, the process of fabricating the resonant structure includes: fabricating a first electrode, a second electrode, and a barrier layer, wherein the first electrode is disposed on the side of the piezoelectric layer near the substrate and exposes at least a portion of the surface of the piezoelectric layer; the second electrode is disposed on the side of the piezoelectric layer away from the substrate; and the barrier layer is disposed between the first electrode and the substrate, covering a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer, wherein a second buffer structure is provided between the piezoelectric layer and the barrier layer in the non-working area, and a third buffer structure is provided between the first electrode and the barrier layer; or the process of fabricating the resonant structure includes: fabricating The piezoelectric layer comprises a first electrode, a second electrode, and a barrier layer, wherein the first electrode is disposed on the side of the piezoelectric layer near the substrate and exposes at least a portion of the surface of the piezoelectric layer, and a first buffer structure is provided between the first electrode and the piezoelectric layer in the non-working region; the second electrode is disposed on the side of the piezoelectric layer away from the substrate; and the barrier layer is disposed between the first electrode and the substrate, covering a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer, and a second buffer structure is provided between the piezoelectric layer and the barrier layer in the non-working region, and a third buffer structure is provided between the first electrode and the barrier layer.

[0020] Optionally, the fabrication method further includes: fabricating a first protective structure and a second protective structure; wherein the first protective structure is disposed on the side surface of the first electrode near the substrate and covers the third buffer structure; and the second protective structure is disposed on the exposed surface of the piezoelectric layer near the substrate and covers the second buffer structure.

[0021] Optionally, the material of the buffer structure is phosphosilicate glass, undoped silicate glass, or borosilicate glass; the film thickness of the buffer structure is 50-500 nm.

[0022] In the bulk acoustic wave filter and its fabrication method for improving film-layer adhesion proposed in this application, the bulk acoustic wave filter includes a substrate and a resonant structure, wherein the resonant structure is disposed on the substrate, and the resonant structure includes a working region and a non-working region surrounding the working region, and a buffer structure is provided between the piezoelectric layer of the resonant structure and the adjacent film layer in the non-working region. By introducing a buffer structure in the non-working region, the stress distribution between the piezoelectric layer and the adjacent film layer is made more uniform, rather than concentrated in certain specific areas (such as at the interface), avoiding stress peaks (i.e., stress concentration) in local areas, reducing the stress difference between the piezoelectric layer and the adjacent film layer, and effectively preventing separation or wafer warping between the piezoelectric layer and the adjacent film, thereby enhancing the robustness and reliability of the device. This solves the technical problem in the prior art where the stress difference between the piezoelectric layer and the adjacent film layer in bulk acoustic wave filters poses a risk of device structural damage and reduced reliability. Attached Figure Description

[0023] The accompanying drawings, which are included to provide a further understanding of this disclosure and form part of this application, illustrate exemplary embodiments of this disclosure and are used to explain this disclosure, but do not constitute an undue limitation of this disclosure. In the drawings:

[0024] Figure 1 This is a schematic diagram of the fabrication process of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 1 of this application;

[0025] Figure 2 This is another structural schematic diagram of the fabrication process of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 1 of this application;

[0026] Figure 3 This is another structural schematic diagram of the fabrication process of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 1 of this application;

[0027] Figure 4 This is another structural schematic diagram of the fabrication process of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 1 of this application;

[0028] Figure 5 This is another structural schematic diagram of the fabrication process of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 1 of this application;

[0029] Figure 6 This is another structural schematic diagram of the fabrication process of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 1 of this application;

[0030] Figure 7 This is another structural schematic diagram of the fabrication process of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 1 of this application;

[0031] Figure 8 This is a schematic diagram of the structure of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 2 of this application;

[0032] Figure 9 This is a schematic diagram of the structure of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 3 of this application;

[0033] Figure 10 This is a schematic diagram of the structure of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 4 of this application;

[0034] Figure 11 This is a schematic diagram of the structure of the bulk acoustic wave filter with improved film adhesion provided in Embodiment 5 of this application;

[0035] Figure 12 This is a schematic diagram of the structure of the bulk acoustic wave filter with improved film bonding provided in Embodiment Six of this application. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solutions of this disclosure, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of this disclosure, and not all embodiments. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0037] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this disclosure are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this disclosure described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0038] Secondly, this application provides a detailed description in conjunction with schematic diagrams. When detailing the embodiments of this application, for ease of explanation, the cross-sectional views illustrating the device structure may be partially enlarged, not adhering to the usual scale. Furthermore, the schematic diagrams are merely examples and should not limit the scope of protection of this application. In addition, actual fabrication should include three-dimensional spatial dimensions of length, width, and depth.

[0039] Terminology definition:

[0040] Working area: refers to the part that directly participates in acoustic wave resonance, usually the overlapping area of ​​the piezoelectric layer and the upper and lower electrodes. The structure is designed to generate and maintain bulk acoustic waves of a specific frequency.

[0041] Non-working area: The structure surrounding the working area is used to support, isolate, and reflect sound waves, prevent energy leakage, suppress unwanted vibration modes, and ensure the performance of the working area.

[0042] As described in the background section, bulk acoustic wave (BAW) filters comprise multiple thin films bonded together to form the filter. However, due to differences in material properties, thermal expansion coefficients, lattice constant mismatches, film thickness variations, and defects and impurities between the piezoelectric layer and adjacent films, a stress difference exists between the piezoelectric layer and adjacent films. This stress difference can lead to separation between the piezoelectric layer and adjacent films or wafer warping, resulting in structural damage to the BAW filter and reduced reliability.

[0043] In view of this, embodiments of this application provide a bulk acoustic wave filter and its fabrication method for improving film layer adhesion. By introducing a buffer structure between the piezoelectric layer of the resonant structure in the non-working region and the adjacent film layer, the stress distribution between the piezoelectric layer and the adjacent film layer is made more uniform, rather than concentrated in certain specific areas (such as the interface), avoiding stress peaks (i.e. stress concentration) in local areas, reducing the stress difference between the piezoelectric layer and the adjacent film layer, and effectively preventing separation between the piezoelectric layer and the adjacent film layer or wafer warping, thereby enhancing the robustness and reliability of the device.

[0044] The following describes the bulk acoustic wave filter with improved film adhesion and its manufacturing method provided in this application, with reference to specific embodiments.

[0045] Example 1

[0046] For ease of understanding, this application first describes the fabrication method of the bulk acoustic wave filter with improved film adhesion. The fabrication method of the bulk acoustic wave filter with improved film adhesion provided in this application includes:

[0047] like Figure 1 As shown, a second electrode layer 110 and a piezoelectric layer 120 are sequentially fabricated on a first substrate 100 used as a temporary substrate. The second electrode layer is used for the subsequent fabrication of a second electrode.

[0048] Optionally, in one embodiment of this application, the first substrate 100 is a silicon substrate, a silicon-on-insulator substrate, a glass substrate, a silicon carbide substrate, or a gallium arsenide (GaAs) substrate, etc.; the second electrode layer 110 can be an Al layer, a Cu layer, a Mo layer, an Au layer, or a Pt layer, and can be formed by physical vapor deposition (PVD); the piezoelectric layer 120 can be an AlN layer, a scandium-doped aluminum nitride (AlxSc1-xN) layer, a lithium niobate (LiNbO3) layer, a lithium tantalate (LiTaO3) layer, or a quartz layer, etc., and can be a polycrystalline layer or a single-crystal layer, and can be formed by PVD or metal-organic chemical vapor deposition (MOCVD), etc.

[0049] like Figure 2 As shown, a buffer structure is formed in the non-working region of the surface of the piezoelectric layer 120 away from the first substrate 100. This buffer structure includes a first buffer structure 132 and a second buffer structure 131.

[0050] Optionally, the material of the buffer structure is phosphosilicate glass (PSG), undoped silicate glass (USG), or borosilicate glass (BPSG), etc.; the film thickness of the buffer structure is 50-500 nm; the stress of the buffer structure is 0±50 MPa; the distance from the boundary of the subsequent sacrificial layer after etching is >2 μm, and the damage to the piezoelectric layer during etching is less than 10 nm; the sidewall angle (profile) of the buffer structure after etching is controlled at 45±15 degrees.

[0051] like Figure 3 As shown, a first electrode layer is formed on the piezoelectric layer 120, and then the first electrode layer is etched to obtain a first electrode 140. The first electrode 140 exposes at least a portion of the surface of the piezoelectric layer 120 and covers the first buffer structure 132. Optionally, the first electrode layer can be an Al layer, Cu layer, Mo layer, Au layer, or Pt layer, and can be formed using a physical vapor deposition (PVD) process.

[0052] Optionally, the resonant structure includes a working region and a non-working region surrounding the working region. A first buffer structure 132 is provided between the first electrode 140 and the piezoelectric layer 120 in the non-working region. The stress value of the first buffer structure 132 is designed to be between the stresses of the first electrode 140 and the piezoelectric layer 120, which can gradually mitigate the stress difference between the first electrode 140 and the piezoelectric layer 120, avoid sudden stress changes at the interface, reduce local stress peaks, and distribute stress more evenly throughout the structure, thereby reducing stress concentration. Furthermore, the material of the first buffer structure 132 is a flexible medium such as phosphosilicate glass (PSG), undoped silicate glass (USG), or borosilicate glass (BPSG), which can absorb and release some stress, reduce stress transmission to adjacent film layers, and reduce stress differences. In addition, the coefficient of thermal expansion of the first buffer structure 132 is between that of the first electrode 140 and the piezoelectric layer 120, which can alleviate thermal stress caused by temperature changes and further reduce stress differences.

[0053] In one embodiment of this application, the etching process for the first electrode layer can be a dry etching process or a wet etching process, but this application does not limit it and it depends on the specific circumstances.

[0054] like Figure 4 As shown, a sacrificial layer 150 is formed in the working region of the first electrode 140 away from the piezoelectric layer 120. The sacrificial layer 150 covers a portion of the exposed surface of the piezoelectric layer 120 and a portion of the surface of the first electrode 140. Optionally, the material of the sacrificial layer 150 can be SiO2, PSG, USG, a-Si, or photoresist, etc.; the formation process of the sacrificial layer 150 can be PVD, CVD, or spin coating, etc.

[0055] like Figure 5 As shown, a fence layer 160 is deposited on the sacrificial layer 150. The fence layer 160 covers the exposed surfaces of the second buffer structure 131, the piezoelectric layer 120, the surface of the sacrificial layer 150, and the exposed surface of the first electrode 140.

[0056] Specifically, a second buffer structure 131 is provided between the fence layer 160 and the piezoelectric layer 120 in the non-working area. The stress value of the second buffer structure 131 is designed to be between the stress values ​​of the fence layer 160 and the piezoelectric layer 120, which can gradually mitigate the stress difference between the fence layer 160 and the piezoelectric layer 120, avoid sudden stress changes at the interface, reduce local stress peaks, and distribute stress more evenly throughout the structure, thereby reducing stress concentration. Furthermore, the material of the second buffer structure 131 is a flexible medium such as phosphosilicate glass (PSG), undoped silicate glass (USG), or borosilicate glass (BPSG), which can absorb and release some stress, reduce stress transmission to adjacent film layers, and reduce stress differences. In addition, the coefficient of thermal expansion of the second buffer structure 131 is between that of the fence layer 160 and the piezoelectric layer 120, which can alleviate thermal stress caused by temperature changes and further reduce stress differences.

[0057] Optionally, the uniformity requirement of the fence layer 160 is <5%.

[0058] Optionally, such as Figure 5 As shown, in the non-working area, the surface of the first electrode 140 away from the first substrate 100 has a raised structure, and the fence layer 160 covers the raised structure and a portion of the flat surface of the first electrode 140 away from the first substrate 100.

[0059] like Figure 6 As shown, a second substrate 170 is bonded to the side of the fence layer 160 away from the piezoelectric layer 120 to serve as a carrier.

[0060] like Figure 7 As shown, the wafer composed of the structures fabricated above is flipped, and the first substrate 100 is removed from the side of the first substrate 100 away from the second substrate 170. Optionally, the removal process of the first substrate 100 can be grinding or chemical mechanical polishing (CMP), which is not limited in this application and depends on the specific circumstances. Then, a portion of the second electrode layer 110 is etched to expose a portion of the surface of the piezoelectric layer 120, forming the second electrode 111.

[0061] Optionally, the etching process of the second electrode layer 110 can be either wet etching or dry etching. The damage to the buffer layer during the etching process of the second electrode layer 110 is less than 10 nm.

[0062] Continue as Figure 7 As shown, the sacrificial layer 150 is released to form a resonant cavity 1501 below the bulk acoustic wave resonator. Optionally, in one embodiment of this application, the operation of releasing the sacrificial layer 150 includes: using liquid phase etching or vapor phase etching to release the sacrificial layer 150 and form the resonant cavity 1501 below the bulk acoustic wave resonator. The damage to the substrate during the etching process of the sacrificial layer 150 is <10nm.

[0063] Specifically, in one embodiment of this application, the sacrificial layer 150 is released using liquid phase etching or vapor phase etching to form a resonant cavity 1501 below the bulk acoustic wave resonator, including:

[0064] The predetermined area of ​​the sacrificial layer is etched using a liquid etching solution such as hydrofluoric acid solution (HF) or buffered oxide etchant (BOE) to form a resonant cavity 1501 below the bulk acoustic resonator.

[0065] Alternatively, the sacrificial layer 150 can be etched using gases such as gaseous hydrogen fluoride (HF) or xenon difluoride (XeF2) to form a resonant cavity 1501 below the bulk acoustic resonator.

[0066] Furthermore, embodiments of this application also provide a bulk acoustic wave filter with improved film adhesion fabricated using the fabrication method provided in any of the above embodiments.

[0067] like Figure 7 As shown, the bulk acoustic wave filter with improved film adhesion provided in this application embodiment includes: a second substrate 170 and a resonant structure, wherein the resonant structure is disposed on the second substrate 170, and the resonant structure includes a working region and a non-working region surrounding the working region, wherein a buffer structure is provided between the piezoelectric layer 120 of the resonant structure and the adjacent film layer in the non-working region.

[0068] Optionally, the resonant structure includes a first electrode 140, a second electrode 111, and a barrier layer 160, wherein the first electrode 140 is disposed on the side of the piezoelectric layer 120 near the second substrate 170 and exposes at least a portion of the surface of the piezoelectric layer 120, and a first buffer structure 132 is provided between the first electrode 140 and the piezoelectric layer 120 in the non-working region; the second electrode 111 is disposed on the side of the piezoelectric layer 120 away from the second substrate 170; and the barrier layer 160 is disposed between the first electrode 140 and the second substrate 170 and covers a portion of the surface of the first electrode 140 near the second substrate 170 and a portion of the exposed surface of the piezoelectric layer 120, and a second buffer structure 131 is provided between the piezoelectric layer 120 and the barrier layer 160 in the non-working region.

[0069] Optionally, in the non-working area, the surface of the first electrode 140 near the second substrate 170 has a raised structure, and the fence layer 160 covers the raised structure and a portion of the flat surface of the first electrode 140 near the second substrate 170.

[0070] It should be noted that since the detailed structure of the bulk acoustic wave filter has been described in detail in the method for manufacturing the bulk acoustic wave filter, it will not be repeated here.

[0071] In summary, the bulk acoustic wave filter and its fabrication method for improving film adhesion proposed in this application include a substrate and a resonant structure. The resonant structure is disposed on the substrate and includes a working region and a non-working region surrounding the working region. Furthermore, a buffer structure is provided between the piezoelectric layer of the resonant structure and adjacent film layers in the non-working region. By introducing a buffer structure in the non-working region, the stress distribution between the piezoelectric layer and adjacent film layers is made more uniform, rather than concentrated in certain specific areas (such as at the interface), avoiding stress peaks (i.e., stress concentration) in local areas. This reduces the stress difference between the piezoelectric layer and adjacent film layers, effectively preventing separation or wafer warping between the piezoelectric layer and adjacent film layers, thereby enhancing the robustness and reliability of the device. This solves the technical problem in the prior art where the stress difference between the piezoelectric layer and adjacent film layers leads to device structural damage and reduced reliability risks in bulk acoustic wave filters.

[0072] Example 2

[0073] The inventive solution in this embodiment is basically the same as that in Embodiment 1, except that, in the inventive solution, as... Figure 8As shown, the bulk acoustic wave filter further includes a first protective structure 182 and a second protective structure 181; wherein the first protective structure 182 is disposed on the surface of the first electrode 140 near the second substrate 170 and covers the protrusion structure; and the second protective structure 181 is disposed on the exposed surface of the piezoelectric layer 120 near the second substrate 170 and covers the second buffer structure 131.

[0074] Specifically, in Example 1 Figure 3 Based on this, a first protective structure 182 is deposited on the first electrode 140, and a second protective structure 181 is deposited on the exposed surface of the piezoelectric layer 120 and the second buffer structure 131. The first protective structure 182 and the second protective structure 181 protect the first electrode 140 and the second buffer structure 131 from damage in subsequent processes.

[0075] Next, following the process flow of Example 1, the sacrificial layer 150, the barrier layer 160, and the second substrate 170 are deposited. Then, the wafer containing the fabricated structures is flipped, and the first substrate 100 is removed from the side of the first substrate 100 away from the second substrate 170. A portion of the second electrode layer 110 is etched to expose a portion of the surface of the piezoelectric layer 120, forming the second electrode 111. Finally, the sacrificial layer 150 is released, thereby obtaining the... Figure 8 The aforementioned bulk acoustic wave filter.

[0076] Example 3

[0077] The inventive solution in this embodiment is basically the same as that in Embodiment 1, except that, in the inventive solution, as... Figure 9 As shown, in the non-working area, no first buffer structure is provided between the first electrode 140 and the piezoelectric layer 120. Instead, a second buffer structure 131 is formed between the fence layer 160 and the piezoelectric layer 120 in the non-working area, and a third buffer structure 133 is formed between the first electrode 140 and the fence layer 160 in the non-working area.

[0078] Specifically, in Example 1 Figure 1 Based on this, a second buffer structure 131 is formed only in the non-working region of the piezoelectric layer 120 on the side away from the first substrate 100. Then, a first electrode layer is fabricated on the piezoelectric layer 120 according to the process flow of Embodiment 1, and the first electrode layer is etched to obtain a first electrode 140. It should be noted that the first electrode 140 in this embodiment does not have a protrusion structure. Subsequently, a third buffer structure 133 is formed on the side of the first electrode 140 in the non-working region away from the piezoelectric layer 120.

[0079] The stress value of the third buffer structure 133 is designed to be between that of the fence layer 160 and the first electrode 140. This gradually mitigates the stress difference between the fence layer 160 and the first electrode 140, preventing sudden stress changes at the interface, reducing local stress peaks, and distributing stress more evenly throughout the structure, thereby reducing stress concentration. The material of the third buffer structure 133 is a flexible medium such as phosphosilicate glass (PSG), undoped silicate glass (USG), or borosilicate glass (BPSG), which can absorb and release some stress, reducing stress transmission to adjacent film layers and lowering stress differences. Furthermore, the coefficient of thermal expansion of the third buffer structure 133 is between that of the fence layer 160 and the first electrode 140, which can alleviate thermal stress caused by temperature changes and further reduce stress differences.

[0080] Next, following the process flow of Embodiment 1, a sacrificial layer 150, a barrier layer 160, and a second substrate 170 are deposited on the piezoelectric layer 120. Then, the wafer containing the fabricated structures is flipped, and the first substrate 100 is removed from the side of the first substrate 100 away from the second substrate 170. A portion of the second electrode layer 110 is etched to expose a portion of the surface of the piezoelectric layer 120, forming the second electrode 111. Finally, the sacrificial layer 150 is released, thereby obtaining the... Figure 9 The aforementioned bulk acoustic wave filter.

[0081] Example 4

[0082] The inventive solution in this embodiment is basically the same as that in Embodiment 3, except that, in the inventive solution, as... Figure 10 As shown, the bulk acoustic wave filter further includes a first protective structure 182 and a second protective structure 181; wherein the first protective structure 182 is disposed on the surface of the first electrode 140 near the second substrate 170 and covers the third buffer structure 133; and the second protective structure 181 is disposed on the exposed surface of the piezoelectric layer 120 near the second substrate 170 and covers the second buffer structure 131.

[0083] Specifically, after fabricating the first substrate 100, piezoelectric layer 120, second buffer structure 131, first electrode 140, and third buffer structure 133 according to the process of Embodiment 3, a first protective structure 182 is deposited on the surface of the first electrode 140 away from the piezoelectric layer 120 and on the third buffer structure 133. A second protective structure 181 is deposited on the exposed surface of the piezoelectric layer 120 and on the second buffer structure 131. The first protective structure 182 and the second protective structure 181 protect the first electrode 140, the third buffer structure 133, and the second buffer structure 131 from damage in subsequent processes.

[0084] Next, following the process flow of Example 3, the sacrificial layer 150, the barrier layer 160, and the second substrate 170 are deposited. Then, the wafer containing the fabricated structures is flipped, and the first substrate 100 is removed from the side of the first substrate 100 away from the second substrate 170. A portion of the second electrode layer 110 is etched to expose a portion of the surface of the piezoelectric layer 120, forming the second electrode 111. Finally, the sacrificial layer 150 is released, thereby obtaining the... Figure 10 The aforementioned bulk acoustic wave filter.

[0085] Example 5

[0086] The inventive solution in this embodiment is basically the same as that in Embodiment 3, except that, in the inventive solution, as... Figure 11 As shown, not only is a second buffer structure 131 formed between the fence layer 160 and the piezoelectric layer 120 in the non-working area, and a third buffer structure 133 formed between the first electrode 140 and the fence layer 160 in the non-working area, but also a first buffer structure 132 is formed between the first electrode 140 and the piezoelectric layer 120 in the non-working area.

[0087] Specifically, in Figure 1 Based on this, a first buffer structure 132 and a second buffer structure 131 are formed in the non-working region of the surface of the piezoelectric layer 120 away from the first substrate 100. Then, a first electrode layer is fabricated on the piezoelectric layer 120 according to the process flow of Embodiment 3, and the first electrode layer is etched to obtain a first electrode 140. It should be noted that the first electrode 140 in this embodiment does not have a protrusion structure. Subsequently, a third buffer structure 133 is formed on the surface of the first electrode 140 in the non-working region away from the piezoelectric layer 120.

[0088] The stress value of the third buffer structure 133 is designed to be between that of the fence layer 160 and the first electrode 140. This gradually mitigates the stress difference between the fence layer 160 and the first electrode 140, preventing sudden stress changes at the interface, reducing local stress peaks, and distributing stress more evenly throughout the structure, thereby reducing stress concentration. The material of the third buffer structure 133 is a flexible medium such as phosphosilicate glass (PSG), undoped silicate glass (USG), or borosilicate glass (BPSG), which can absorb and release some stress, reducing stress transmission to adjacent film layers and lowering stress differences. Furthermore, the coefficient of thermal expansion of the third buffer structure 133 is between that of the fence layer 160 and the first electrode 140, which can alleviate thermal stress caused by temperature changes and further reduce stress differences.

[0089] Next, following the process flow of Embodiment 3, a sacrificial layer 150, a barrier layer 160, and a second substrate 170 are deposited on the piezoelectric layer 120. Then, the wafer containing the fabricated structures is flipped, and the first substrate 100 is removed from the side of the first substrate 100 away from the second substrate 170. A portion of the second electrode layer 110 is etched to expose a portion of the surface of the piezoelectric layer 120, forming the second electrode 111. Finally, the sacrificial layer 150 is released, thereby obtaining the desired structure. Figure 11 The aforementioned bulk acoustic wave filter.

[0090] Example 6

[0091] The inventive solution in this embodiment is basically the same as that in Embodiment 5, except that, in the inventive solution, as... Figure 12 As shown, the bulk acoustic wave filter further includes a first protective structure 182 and a second protective structure 181; wherein the first protective structure 182 is disposed on the surface of the first electrode 140 near the second substrate 170 and covers the third buffer structure 133; and the second protective structure 181 is disposed on the exposed surface of the piezoelectric layer 120 near the second substrate 170 and covers the second buffer structure 131.

[0092] Specifically, after fabricating the first substrate 100, piezoelectric layer 120, first buffer structure 132, second buffer structure 131, first electrode 140, and third buffer structure 133 according to the process of Embodiment 5, a first protective structure 182 is deposited on the surface of the first electrode 140 away from the piezoelectric layer 120 and on the third buffer structure 133. A second protective structure 181 is deposited on the exposed surface of the piezoelectric layer 120 and on the second buffer structure 131. The first protective structure 182 and the second protective structure 181 protect the first electrode 140, the third buffer structure 133, and the second buffer structure 131 from damage in subsequent processes.

[0093] Next, following the process flow of Example 5, the sacrificial layer 150, the barrier layer 160, and the second substrate 170 are deposited. Then, the wafer containing the fabricated structures is flipped, and the first substrate 100 is removed from the side of the first substrate 100 away from the second substrate 170. A portion of the second electrode layer 110 is etched to expose a portion of the surface of the piezoelectric layer 120, forming the second electrode 111. Finally, the sacrificial layer 150 is released, thereby obtaining the... Figure 12 The aforementioned bulk acoustic wave filter.

[0094] In summary, the bulk acoustic wave filter and its fabrication method for improving film adhesion proposed in this application include a substrate and a resonant structure. The resonant structure is disposed on the substrate and includes a working region and a non-working region surrounding the working region. Furthermore, a buffer structure is provided between the piezoelectric layer of the resonant structure and adjacent film layers in the non-working region. By introducing a buffer structure in the non-working region, the stress distribution between the piezoelectric layer and adjacent film layers is made more uniform, rather than concentrated in certain specific areas (such as at the interface), avoiding stress peaks (i.e., stress concentration) in local areas. This reduces the stress difference between the piezoelectric layer and adjacent film layers, effectively preventing separation or wafer warping between the piezoelectric layer and adjacent film layers, thereby enhancing the robustness and reliability of the device. This solves the technical problem in the prior art where the stress difference between the piezoelectric layer and adjacent film layers leads to device structural damage and reduced reliability risks in bulk acoustic wave filters.

[0095] The various sections in this manual are described in a progressive manner, with each section focusing on the differences from the others. Similar or identical parts can be referred to each other.

[0096] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A bulk acoustic wave filter with improved film layer adhesion, characterized in that, include: A substrate and a resonant structure, wherein the resonant structure is disposed on the substrate and the resonant structure includes a working region and a non-working region surrounding the working region, wherein in the non-working region the piezoelectric layer of the resonant structure has a first buffer structure between itself and an adjacent first electrode and a second buffer structure between itself and an adjacent fence layer.

2. The bulk acoustic wave filter according to claim 1, characterized in that, The resonant structure includes a first electrode, a second electrode, and a fence layer, wherein... The first electrode is disposed on the side of the piezoelectric layer close to the substrate and exposes at least a portion of the surface of the piezoelectric layer. In the non-working area, a first buffer structure is provided between the first electrode and the piezoelectric layer. The second electrode is disposed on the side of the piezoelectric layer away from the substrate; as well as The fence layer is disposed between the first electrode and the substrate, and covers a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer. A second buffer structure is provided between the piezoelectric layer and the fence layer in the non-working area.

3. The bulk acoustic wave filter according to claim 2, characterized in that, In the non-working area, the surface of the first electrode near the substrate has a raised structure, and the fence layer covers the raised structure and a portion of the flat surface of the first electrode near the substrate.

4. The bulk acoustic wave filter according to claim 3, characterized in that, The bulk acoustic wave filter further includes a first protection structure and a second protection structure; wherein The first protective structure is disposed on the surface of the first electrode near the substrate and covers the protruding structure; and The second protective structure is disposed on the exposed surface of the piezoelectric layer near the substrate and covers the second buffer structure.

5. The bulk acoustic wave filter according to claim 1, characterized in that, The resonant structure includes a first electrode, a second electrode, and a fence layer, wherein... The first electrode is disposed on the side of the piezoelectric layer close to the substrate and exposes at least a portion of the surface of the piezoelectric layer; The second electrode is disposed on the side of the piezoelectric layer away from the substrate; as well as The fence layer is disposed between the first electrode and the substrate, and covers a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer. In the non-working area, there is a second buffer structure between the piezoelectric layer and the fence layer, and a third buffer structure between the first electrode and the fence layer.

6. The bulk acoustic wave filter according to claim 1, characterized in that, The resonant structure includes a first electrode, a second electrode, and a fence layer, wherein... The first electrode is disposed on the side of the piezoelectric layer close to the substrate and exposes at least a portion of the surface of the piezoelectric layer. In the non-working area, a first buffer structure is provided between the first electrode and the piezoelectric layer. The second electrode is disposed on the side of the piezoelectric layer away from the substrate; as well as The fence layer is disposed between the first electrode and the substrate, and covers a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer. In the non-working area, there is a second buffer structure between the piezoelectric layer and the fence layer and a third buffer structure between the first electrode and the fence layer.

7. The bulk acoustic wave filter according to claim 5 or 6, characterized in that, The resonant structure further includes a first protective structure and a second protective structure; wherein The first protective structure is disposed on the surface of the first electrode near the substrate and covers the third buffer structure; and The second protective structure is disposed on the exposed surface of the piezoelectric layer near the substrate and covers the second buffer structure.

8. The bulk acoustic wave filter according to claim 1, characterized in that, The material of the buffer structure is phosphosilicate glass, undoped silicate glass, or borophosphosilicate glass.

9. The bulk acoustic wave filter according to claim 1, characterized in that, The thickness of the buffer structure is 50-500 nm.

10. A method for fabricating a bulk acoustic wave filter with improved film layer adhesion, characterized in that, include: A substrate and a resonant structure are fabricated, wherein the resonant structure is disposed on the substrate, and the resonant structure includes a working region and a non-working region surrounding the working region, wherein in the non-working region the piezoelectric layer of the resonant structure has a first buffer structure between itself and an adjacent first electrode and a second buffer structure between itself and an adjacent fence layer.

11. The manufacturing method according to claim 10, characterized in that, The process of fabricating the resonant structure includes: fabricating a first electrode, a second electrode, and a fence layer, wherein the first electrode is disposed on the side of the piezoelectric layer near the substrate and exposes at least a portion of the surface of the piezoelectric layer; a first buffer structure is provided between the first electrode and the piezoelectric layer in the non-working region; the second electrode is disposed on the side of the piezoelectric layer away from the substrate; and the fence layer is disposed between the first electrode and the substrate, covering a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer; a second buffer structure is provided between the piezoelectric layer and the fence layer in the non-working region; a protruding structure is provided on the surface of the first electrode near the substrate in the non-working region, and the fence layer covers the protruding structure and a portion of the flat surface of the first electrode near the substrate; and The fabrication method further includes: fabricating a first protective structure and a second protective structure; wherein the first protective structure is disposed on the side surface of the first electrode near the substrate and covers the protrusion structure; and the second protective structure is disposed on the exposed surface of the piezoelectric layer near the substrate and covers the second buffer structure.

12. The manufacturing method according to claim 10, characterized in that, The process of fabricating the resonant structure includes: fabricating a first electrode, a second electrode, and a barrier layer, wherein the first electrode is disposed on the side of the piezoelectric layer near the substrate and exposes at least a portion of the surface of the piezoelectric layer; the second electrode is disposed on the side of the piezoelectric layer away from the substrate; and the barrier layer is disposed between the first electrode and the substrate, covering a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer, wherein a second buffer structure is provided between the piezoelectric layer and the barrier layer in the non-working region, and a third buffer structure is provided between the first electrode and the barrier layer; or The process of fabricating the resonant structure includes: fabricating a first electrode, a second electrode, and a fence layer, wherein the first electrode is disposed on the side of the piezoelectric layer near the substrate and exposes at least a portion of the surface of the piezoelectric layer, and a first buffer structure is provided between the first electrode and the piezoelectric layer in the non-working region; the second electrode is disposed on the side of the piezoelectric layer away from the substrate; and the fence layer is disposed between the first electrode and the substrate, and covers a portion of the surface of the first electrode near the substrate and a portion of the exposed surface of the piezoelectric layer, a second buffer structure is provided between the piezoelectric layer and the fence layer in the non-working region, and a third buffer structure is provided between the first electrode and the fence layer.

13. The manufacturing method according to claim 12, characterized in that, The fabrication method further includes: fabricating a first protective structure and a second protective structure; wherein the first protective structure is disposed on the side surface of the first electrode near the substrate and covers the third buffer structure; and the second protective structure is disposed on the exposed surface of the piezoelectric layer near the substrate and covers the second buffer structure.

14. The manufacturing method according to claim 10, characterized in that, The material of the buffer structure is phosphosilicate glass, undoped silicate glass, or borosilicate glass; the film thickness of the buffer structure is 50-500 nm.

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