A cavity type bulk acoustic resonator and a method of manufacturing the same

Abstract

The application discloses the technical field of resonators, and discloses a cavity bulk acoustic resonator and a preparation method thereof. The cavity bulk acoustic resonator comprises a first substrate, a support layer, a lower electrode layer, a piezoelectric layer, an upper electrode layer and an acoustic reflection structure layer. The support layer has a cavity formed by concave in the upper surface. The acoustic reflection structure layer comprises a lower acoustic reflection structure layer and an upper acoustic reflection structure layer. The lower acoustic reflection structure layer and the upper acoustic reflection structure layer are both closed structures. The lower electrode layer fills the inside of the lower acoustic reflection structure layer and covers the surface of the lower acoustic reflection structure layer. The upper electrode layer fills the inside of the upper acoustic reflection structure layer and covers the surface of the upper acoustic reflection structure layer. The application can effectively inhibit the energy dissipation from the edge of the resonant area during the resonance of the resonator and the filter, and further improves the Q value of the resonator based on the piezoelectric thin film of the gallium oxide epitaxial material.

Description

Technical Field

[0001] This invention relates to the field of resonator technology, and in particular to a cavity-type bulk acoustic resonator and its fabrication method. Background Technology

[0002] 5G communication technology needs to cope with complex multi-user simultaneous communication scenarios, which places higher demands on the performance of filters in communication systems. Specifically, 5G filters not only need to improve performance requirements to meet indicators such as multi-band, wide bandwidth, low insertion loss, and high isolation, but also need to adapt to the development trend of integration and miniaturization to be compatible with high-density packaged communication equipment.

[0003] The core performance of a filter largely depends on the quality factor (Q value) of its internal resonator. A higher Q value results in lower energy loss in the resonator and better selectivity and stability of the filter. Therefore, in 5G communication systems, achieving high-performance 5G filters places significantly higher demands on resonator performance, especially the Q value. Effectively improving the quality factor of the resonator has become a key focus and urgent issue for the industry.

[0004] Currently, the mainstream approach to improving the Q-value of bulk acoustic wave resonators and filters in the industry primarily relies on aluminum nitride (AlN) piezoelectric materials prepared using physical vapor deposition (PVD) technology. While this method can improve the Q-value to some extent, it lacks effective solutions for resonator structures based on epitaxially grown piezoelectric materials. Epitaxially grown piezoelectric materials possess unique crystal structures and performance advantages; however, existing technologies struggle to fully realize their potential and cannot effectively reduce energy dissipation during resonance through reasonable structural design. This limits the improvement of the Q-value of such resonators, thereby affecting the application performance of filters based on these materials in 5G communication systems.

[0005] Therefore, developing an innovative solution for resonator structures based on epitaxially grown piezoelectric materials that can effectively control energy loss and improve their quality factor is of great significance for further improving the performance of 5G filters. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a cavity-type bulk acoustic resonator and its preparation method, which can suppress the energy dissipation from the edge of the resonant region during the resonance process of the resonator and filter, and improve the Q value of the resonator based on piezoelectric thin films of epitaxial materials such as gallium oxide.

[0007] To address the aforementioned technical problems, a first aspect of the present invention provides a cavity-type bulk acoustic resonator, comprising: First substrate, A support layer is bonded to the first substrate, and the support layer has a cavity formed by an indentation in its upper surface; A lower electrode layer that covers the surface of the support layer above the cavity; A piezoelectric layer is disposed on the upper surface of the lower electrode layer and in contact with the support layer; An upper electrode layer is disposed on the upper surface of the piezoelectric layer; The acoustic reflection structure layer includes a lower acoustic reflection structure layer and an upper acoustic reflection structure layer, both of which are closed structures. The lower electrode layer fills the interior of the lower acoustic reflection structure layer and covers its surface, while the upper electrode layer fills the interior of the upper acoustic reflection structure layer and covers its surface.

[0008] As an improvement to the above scheme, the lower electrode layer and the upper electrode layer are correspondingly arranged, and the geometric center axes of the lower electrode layer and the upper electrode layer overlap, with the lower electrode layer completely covering the effective resonant region of the upper electrode layer.

[0009] As an improvement to the above scheme, the upper acoustic reflection structure layer overlaps with the geometric center axis of the upper electrode layer, the lower acoustic reflection structure layer overlaps with the geometric center axis of the upper electrode layer, and the inner boundary of the lower acoustic reflection structure layer is located outside the edge projection range of the effective resonant area coverage area of ​​the upper electrode layer.

[0010] As an improvement to the above scheme, the inner boundary of the lower acoustic reflection structure layer is located between the inner boundary and the outer edge of the upper acoustic reflection structure layer, so that the projection of the lower electrode layer on the plane completely covers the effective resonant region of the upper electrode layer.

[0011] As an improvement to the above scheme, the distance between the inner boundary of the lower acoustic reflection structure layer and the outer edge of the upper acoustic reflection structure layer is 0.5μm-3μm; The distance between the inner boundary of the lower acoustic reflection structure layer and the inner boundary of the upper acoustic reflection structure layer is 0.5μm-3μm; The distance between the outer edge of the lower acoustic reflection structure layer and the outer edge of the upper acoustic reflection structure layer is 0.5μm-2μm; As an improvement to the above solution, the lower electrode layer is also disposed outside the lower acoustic reflection structure layer and covers part of the outer side of the lower acoustic reflection structure layer; The distance between the outer edge of the lower acoustic reflection structure layer and the outer edge of the lower electrode layer is 1μm-10μm; The thickness of the lower acoustic reflection structure layer is 10nm-500nm, and the width of the lower acoustic reflection structure layer is 0.5μm-3μm; the thickness of the lower electrode layer is 100nm-500nm.

[0012] As an improvement to the above solution, the outer edge of the upper acoustic reflection structure layer coincides with the outer edge of the upper electrode layer; The thickness of the upper acoustic reflection structure layer is 50nm-500nm, and the width of the upper acoustic reflection structure layer is controlled between 0.5μm and 5μm. The thickness of the upper electrode layer is 100nm-1000nm.

[0013] As an improvement to the above solution, the projection of the lower electrode layer on the plane completely covers the entire area of ​​the cavity, and the distance between the outer edge of the lower electrode layer and the sidewall of the cavity is greater than 3μm; The distance between the sidewall of the cavity and the outer edge of the lower acoustic reflection structure layer is 1μm-5μm; The thickness of the cavity is 0.5μm-5μm.

[0014] As an improvement to the above solution, the acoustic reflection structure layer is a closed ring structure; The first substrate includes a substrate layer and a surface bonding layer disposed on the substrate layer. The substrate layer is made of one or more of silicon, sapphire, silicon carbide, and diamond. The surface bonding layer is made of at least one of silicon and silicon dioxide. The support material of the support layer is one or more of silicon and ceramic; The material of the lower electrode layer is one or more of molybdenum, aluminum, and tungsten; The piezoelectric layer is made of one or more of aluminum nitride and gallium oxide. The material of the upper electrode layer is one or more of molybdenum, aluminum, and tungsten; The material of the acoustic reflection structure layer is one or more of molybdenum, aluminum, and tungsten.

[0015] A second aspect of the present invention also provides a method for fabricating the cavity-type bulk acoustic resonator, comprising the following steps: A temporary substrate is provided, and a piezoelectric layer is fabricated on the temporary substrate; A lower acoustic reflection structure layer and a lower electrode layer are fabricated on the piezoelectric layer, such that the lower electrode layer fills the interior of the lower acoustic reflection structure layer and covers the lower acoustic reflection structure layer. A filling layer is prepared on the lower electrode layer and the lower acoustic reflection structure layer, and the projection of the filling layer on the plane is completely located within the effective resonant region of the lower electrode layer. A support layer is prepared on the filler layer and the piezoelectric layer not covered by the filler layer, and then planarized. A first substrate is provided, and the first substrate is bonded to the support layer; Remove the temporary substrate to expose the piezoelectric layer; An upper acoustic reflection structure layer and an upper electrode layer are prepared on the exposed piezoelectric layer, such that the upper electrode layer fills the interior of the upper acoustic reflection structure layer and covers the surface of the upper acoustic reflection structure layer; Remove the filling layer to form a cavity.

[0016] Implementing this invention has the following beneficial effects: In this application, based on the original epitaxial cavity resonator, an upper acoustic reflection structure layer and a lower acoustic reflection structure layer are provided at the relevant positions of the upper electrode layer and the lower electrode layer. This can effectively suppress the energy dissipation from the edge of the resonant region during the resonance process of the resonator and the filter, and further improve the Q value of the resonator based on piezoelectric thin films such as gallium oxide. Attached Figure Description

[0017] Figure 1: A cross-sectional structural schematic diagram of a cavity-type bulk acoustic resonator according to the present invention; Figure 2: A magnified view of part A in Figure 1; Figure 3: Top view schematic diagram of a cavity-type solid acoustic resonator according to the present invention. Figure 4: A cross-sectional view of the structure obtained in step (1) of this invention; Figure 5: A cross-sectional view of the structure obtained in step (21) of this invention; Figure 6: A cross-sectional view of the structure obtained in step (22) of this invention; Figure 7: A cross-sectional view of the structure obtained in step (3) of this invention; Figure 8: A cross-sectional view of the structure obtained before planarization in step (4) of this invention; Figure 9: A cross-sectional view of the structure obtained after planarization in step (4) of this invention; Figure 10: A cross-sectional view of the structure obtained in step (5) of this invention; Figure 11: A cross-sectional view of the structure obtained in step (6) of this invention; Figure 12: Schematic diagram of the structure of the acoustic reflection structure material forming layer in step (71) of the present invention; Figure 13: A cross-sectional view of the structure obtained in step (71) of this invention; Figure 14: A cross-sectional view of the structure obtained in step (72) of this invention; Figure 15: Test results of the impedance of the cavity-type bulk acoustic resonator obtained in Embodiment 1 of the present invention; Figure 16: Test results of the Q value of the cavity-type bulk acoustic resonator obtained in Example 1 of the present invention.

[0018] Figure label: 1-First substrate; 2-Support layer; 3-Cavity; 4-Lower electrode layer; 5-Piezoelectric layer; 6-Upper electrode layer; 7-Acoustic reflection structure layer; 71-Lower acoustic reflection structure layer; 72-Upper acoustic reflection structure layer; 8-Temporary substrate; 9-Filling layer. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the present invention clearer, specific embodiments will be described in further detail below.

[0020] In the description of this application, it is necessary to understand that the orientation or positional relationship indicated by terms such as "upper", "lower", "top", "bottom", "inner", and "outer" are based on the orientation or positional relationship shown in the accompanying drawings. They are intended only to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the components referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0021] To address the aforementioned problems, the first aspect of this invention provides a cavity-type bulk acoustic resonator, as shown in Figures 1-3, comprising: a first substrate 1, a support layer 2, a lower electrode layer 4, a piezoelectric layer 5, an upper electrode layer 6, and an acoustic reflection structure layer 7. The support layer 2 is bonded to the first substrate 1 and has a cavity 3 formed by an indentation in its upper surface. The lower electrode layer 4 covers the surface of the support layer 2 above the cavity 3. The piezoelectric layer 5 is disposed on the upper surface of the lower electrode layer 4 and contacts the support layer 2. The acoustic reflection structure layer 7 includes a lower acoustic reflection structure layer 71 and an upper acoustic reflection structure layer 72, both of which are closed structures. The lower electrode layer 4 fills the interior of the lower acoustic reflection structure layer 71 and covers its surface. The upper electrode layer 6 fills the interior of the upper acoustic reflection structure layer 72 and covers its surface.

[0022] In this application, based on the original epitaxial cavity resonator, an upper acoustic reflection structure layer 72 and a lower acoustic reflection structure layer 71 are provided at the relevant positions of the upper electrode layer 6 and the lower electrode layer 4. This can effectively suppress the energy dissipation from the edge of the resonant region during the resonance process of the resonator and the filter, and further improve the Q value of the resonator based on piezoelectric thin films such as gallium oxide.

[0023] Specifically, the lower electrode layer 4 and the upper electrode layer 6 are correspondingly arranged, and the geometric center axes of the lower electrode layer 4 and the upper electrode layer 6 overlap. The lower electrode layer 4 completely covers the effective resonant region of the upper electrode, which can ensure stable propagation within the acoustic resonator, optimize the acoustic reflection path, reduce energy loss, reduce signal interference, and improve the overall performance and stability of the resonator.

[0024] Furthermore, the upper acoustic reflection structure layer 72 overlaps with the geometric center axis of the upper electrode layer 6, and the lower acoustic reflection structure layer 71 overlaps with the geometric center axis of the upper electrode layer 6. The inner boundary of the lower acoustic reflection structure layer 71 is located outside the edge projection range of the effective resonant area covered by the upper electrode layer 6. This can form a symmetrical standing wave within the piezoelectric layer 5, reduce modal distortion, capture transverse acoustic waves scattered from the electrode edge, and improve reflection efficiency and Q value.

[0025] More preferably, the inner boundary of the lower acoustic reflection structure layer 71 is located between the inner boundary and the outer edge of the upper acoustic reflection structure layer 72, so that the projection of the lower electrode layer 4 on the plane completely covers the effective resonant region of the upper electrode layer 6, further improving the resonant frequency, while avoiding the overlap of the upper electrode layer 6 and the lower electrode layer 4, thereby reducing signal interference.

[0026] In some specific and preferred embodiments, the distance W1 between the inner boundary of the lower acoustic reflection structure layer 71 and the outer edge of the upper acoustic reflection structure layer 72 is 0.5μm-3μm, exemplarily 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, and 3μm, but not limited thereto; the distance W2 between the inner boundary of the lower acoustic reflection structure layer 71 and the inner boundary of the upper acoustic reflection structure layer 72 is 0.5μm-3μm, exemplarily 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, and 3μm, but not limited thereto; the distance W3 between the outer edge of the lower acoustic reflection structure layer 71 and the outer edge of the upper acoustic reflection structure layer 72 is 0.5μm-2μm.

[0027] Preferably, the lower electrode layer 4 is also disposed outside the lower acoustic reflection structure layer 71 and covers part of the outer side of the lower acoustic reflection structure layer 71, expanding the electric field coverage range, reducing edge electric field distortion, improving the stability of the resonant frequency, and forming protrusions near the two ends of the lower electrode layer 4. The outer electrode layer can be used to receive and reflect sound waves, forming a high acoustic impedance abrupt change region, enhancing the reflection efficiency of longitudinal sound waves, reducing energy leakage to the substrate, and allowing the energy to be concentrated in the effective resonant region, thereby improving the Q value.

[0028] Optionally, the distance W4 between the outer edge of the lower acoustic reflection structure layer 71 and the outer edge of the lower electrode layer 4 is 1μm-10μm, which can optimize the constraint of acoustic wave energy and further improve the Q value. If the distance is too small, it will increase the acoustic capacitance effect, resulting in resonant frequency shift and stray mode coupling. The distance W4 between the outer edge of the lower acoustic reflection structure layer 71 and the outer edge of the lower electrode layer 4 are exemplarily 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, and 10μm.

[0029] Optionally, the thickness H1 of the lower acoustic reflection structure layer 71 is 10nm-500nm, and the width W5 of the lower acoustic reflection structure layer 71 is 0.5μm-3μm; the thickness H2 of the lower electrode layer 4 is 100nm-500nm. Through the synergistic cooperation of multiple parameters, not only can the Q value be improved, but the local stress of the piezoelectric layer 5 can also be avoided. If the thickness of the lower acoustic reflection structure layer 71 is too large, it will aggravate the local stress of the piezoelectric layer 5 and induce cracks. If the thickness of the lower electrode layer 4 is too large, although it will enhance the conductivity of the electrode, it will also lead to thermal expansion mismatch and an increase in the temperature drift coefficient. The thickness H1 of the lower acoustic reflection structure layer 71 is, for example, 10nm, 50nm, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 450nm, or 500nm, but is not limited thereto; the width W5 of the lower acoustic reflection structure layer 71 is, for example, 0.5μm, 1μm, 1.5μm, 2μm, 2.5μm, or 3μm, but is not limited thereto; the thickness H2 of the lower electrode layer 4 is, for example, 100nm, 150nm, 200nm, 250nm, 300nm, 350nm, 450nm, or 500nm, but is not limited thereto.

[0030] Preferably, the outer edge of the upper acoustic reflection structure layer 72 coincides with the outer edge of the upper electrode layer 6. By increasing the thickness of the upper electrode layer 6 to form the upper acoustic reflection structure layer 72, the energy dissipation during the resonance process can be further reduced, the sound wave reflection effect can be significantly enhanced, and the sound wave can be efficiently transmitted between the upper electrode layer 6 and the upper acoustic reflection structure layer 72, thereby improving the Q value of the resonator and the filter.

[0031] Furthermore, the thickness H3 of the upper acoustic reflection structure layer 72 is 50nm-500nm, the width W6 of the upper acoustic reflection structure layer 72 is controlled between 0.5μm and 5μm, and the thickness H4 of the upper electrode layer 6 is 100nm-1000nm. Through the coordinated operation of the three, it is ensured that the sound wave will not be lost due to the thickness difference during reflection, thus maintaining the sound wave efficiency. Moreover, it can also effectively prevent sound wave leakage and achieve the best sound wave reflection effect.

[0032] Preferably, the projection of the lower electrode layer 4 onto the plane completely covers the entire area of ​​the cavity 3, and the distance W7 between the outer edge of the lower electrode layer 4 and the sidewall of the cavity 3 is greater than 3 μm, and the distance W8 between the sidewall of the cavity 3 and the outer edge of the lower acoustic reflection structure layer 71 is 1 μm-5 μm. Based on this design, it is helpful to adjust the angle and path of acoustic wave reflection, reduce the loss of acoustic waves during the reflection process, maximize the reflection efficiency of acoustic waves, enhance the intensity of acoustic waves, and thus improve the performance of the entire device.

[0033] Furthermore, the thickness H5 of the cavity 3 is 0.5μm-5μm. This thickness enhances the sound wave reflection effect of the lower acoustic reflection structure layer 71, ensuring effective sound wave transmission within the structure. Combined with the spacing between the sidewall of the cavity 3 and the outer edge of the lower acoustic reflection structure layer 71, it significantly improves the overall acoustic performance of the structure. The thickness H5 of the cavity 3 is exemplarily 0.5μm, 1μm, 2μm, 3μm, 4μm, or 5μm, but is not limited to these.

[0034] Optionally, the material of the acoustic reflection structure layer 7 is a metallic material, including but not limited to molybdenum, aluminum, and tungsten. The material of the upper acoustic reflection structure layer 72 and the lower acoustic reflection structure layer 71 can be the same material or different materials. The acoustic reflection structure layer 7 is preferably a closed ring structure. Of course, the acoustic reflection structure 7 can also be a closed structure of other shapes, such as a square.

[0035] Optionally, the materials of the upper electrode layer 6 and the lower electrode layer 4 are also metallic materials. Specifically, the materials of the upper electrode layer 6 and the lower electrode layer 4 can be at least one of molybdenum, aluminum, and tungsten. The materials of the upper electrode layer 6 and the lower electrode layer 4 can be the same or different.

[0036] Accordingly, the present invention also provides a method for fabricating the cavity-type bulk acoustic resonator, comprising the following steps: (1) A temporary substrate 8 is provided, and a piezoelectric layer 5 is prepared on the temporary substrate 8; (2) A lower acoustic reflection structure layer 71 and a lower electrode layer 4 are prepared on the piezoelectric layer 5, such that the lower electrode layer 4 fills the interior of the lower acoustic reflection structure layer 71 and covers the lower acoustic reflection structure layer 71. (3) A filling layer 9 is prepared on the lower electrode layer 4 and the lower acoustic reflection structure layer 71, wherein the projection of the filling layer 9 on the plane is completely located within the effective resonant region of the lower electrode layer 4; (4) A support layer 2 is prepared on the filling layer 9 and the piezoelectric layer 5 not covered by the filling layer 9, and the support layer 2 is planarized. (5) Provide a first substrate 1, and bond the first substrate 1 to the support layer 2; (6) Remove the temporary substrate 8 to expose the piezoelectric layer 5; (7) An upper acoustic reflection structure 72 and an upper electrode layer 6 are prepared on the exposed piezoelectric layer 5, such that the upper electrode layer 6 fills the interior of the upper acoustic reflection structure layer 72 and covers the upper acoustic reflection structure layer 72. (8) Remove the filling layer 9 to form a cavity 3.

[0037] Each step will be explained in detail below.

[0038] Regarding step (1), a temporary substrate 8 is provided, and a piezoelectric layer 5 is prepared on the temporary substrate 8; Please refer to Figure 4. In this step, a piezoelectric layer 5 is prepared on the temporary substrate 8 to form an epitaxial wafer structure. The deposition thickness of the piezoelectric layer 5 is 200nm-1000nm. The preparation process of the piezoelectric layer 5 includes, but is not limited to, metal-organic chemical vapor deposition (MOCVD).

[0039] Optionally, the temporary substrate 8 may be made of one or more of the following materials: sapphire, silicon carbide, silicon nitride, and silicon.

[0040] Optionally, the piezoelectric layer 5 is made of a single-crystal thin-film material, specifically aluminum nitride, epsilon-phase gallium oxide, etc. More preferably, the piezoelectric layer 5 is made of epsilon-phase gallium oxide, which has higher electromechanical conversion efficiency.

[0041] Regarding step (2), a lower acoustic reflection structure layer 71 and a lower electrode layer 4 are prepared on the piezoelectric layer 5, such that the lower electrode layer 4 fills the interior of the lower acoustic reflection structure layer 71 and covers the lower acoustic reflection structure layer 71. This step specifically includes: (21) A lower acoustic reflection structure layer 71 is fabricated on the piezoelectric layer 5; For example, a lower acoustic reflection structure material is deposited on the piezoelectric layer 5 to form a layer structure. Then, photoresist is applied to the surface of the layer structure. After exposure and development, the part to be etched is etched to form a lower acoustic reflection structure layer 71 with a closed-loop structure, as shown in Figure 5.

[0042] Optionally, the deposition process of the lower acoustic reflection structure layer 71 includes, but is not limited to, physical vapor deposition (PVD), evaporation, etc., and the material of the lower acoustic reflection structure layer 71 is a metallic material, including but not limited to molybdenum, aluminum, and tungsten.

[0043] (22) A lower electrode layer 4 is prepared on the piezoelectric layer 5, such that the lower electrode layer 4 fills the interior of the lower acoustic reflection structure layer 71 and covers the outside of the lower acoustic reflection structure layer 71; For example, the lower electrode material is deposited on the piezoelectric layer 5 and the lower acoustic reflection structure layer 71 to form a layer structure. Then, photoresist is applied to the surface of the layer structure. After exposure and development, the part to be etched is etched so that the lower electrode layer 4 is located inside and outside the lower acoustic reflection structure layer 71 and is deposited on the lower acoustic reflection structure layer 71 to form a protruding structure, as shown in Figure 6.

[0044] In this step, the lower electrode layer 4 overlaps with the geometric center axis of the lower acoustic reflection structure layer 71, and the distance between the outer edge of the lower acoustic reflection structure layer 71 and the outer edge of the lower electrode layer 4 is 1μm-10μm.

[0045] Optionally, the deposition process of the lower electrode layer 4 includes, but is not limited to, PVD, and the lower electrode material is a metallic material, including but not limited to molybdenum, aluminum, and tungsten.

[0046] Regarding step (3), a filling layer 9 is prepared on the lower electrode layer 4 and the lower acoustic reflection structure layer 71, and the projection of the filling layer 9 on the plane is completely located within the effective resonance region of the lower electrode layer 4. In this step, filler is deposited on the surfaces of the lower electrode layer 4, the lower acoustic reflection structure layer 71 not covered by the lower electrode layer 4, and the piezoelectric layer 5 to form a layer structure. Then, a photoresist layer is coated on the surface of the layer structure. After exposure and development, the part to be etched is etched until the piezoelectric layer 5 and part of the lower electrode layer 4 are exposed to form a filler layer 9. The filler layer 9 covers the lower acoustic reflection structure layer 71, and the outer edge contour of the filler layer 9 on the horizontal projection plane is completely within the outer edge contour of the resonant region of the lower electrode layer 4, as shown in Figure 7.

[0047] Furthermore, the thickness of the filling layer 9 is 0.5μm-5μm, the distance between the outer edge of the filling layer 9 and the outer edge of the lower electrode layer 4 is greater than 3μm, and the distance between the outer edge of the filling layer 9 and the outer edge of the lower acoustic reflection structure layer 71 is 1μm-5μm.

[0048] Optionally, the deposition process of the filling layer 9 can be chemical vapor deposition (CVD), spin coating, etc., and the filler can be materials such as silicon dioxide and resin, wherein the silicon dioxide is specifically conventional silicon dioxide, phosphorus-containing silicon dioxide, etc.

[0049] Regarding step (4), a support layer 2 is prepared on the filling layer 9 and the piezoelectric layer 5 not covered by the filling layer 9, and then planarized. In this step, the support layer 2 is provided to support the formation of the cavity 3 and facilitate bonding with the first substrate 1. Therefore, a material is deposited on the filling layer 9 and the piezoelectric layer 5 not covered by the filling layer 9, so that the support layer 2 completely covers the filling layer 9 and forms a certain thickness. Thus, the thickness of the support layer 2 is greater than the sum of the thicknesses of the lower electrode layer 4 and the filling layer 9, as shown in Figure 8.

[0050] Furthermore, the sum of the thicknesses of the lower electrode layer 4 and the filling layer 9 is generally controlled to be above 300 nm, and the thickness of the support layer 2 is controlled to be between 2 μm and 10 μm. The support material of the support layer 2 includes, but is not limited to, silicon, ceramics, etc.

[0051] Optionally, the deposition process of the support layer 2 includes, but is not limited to, CVD, PVD, etc. However, due to the setting of the filler layer 9 and the filled lower acoustic reflection structure layer 71, the height of the formed support layer 2 is not uniform. Therefore, the formed support layer 2 needs to be planarized to make its height uniform in preparation for subsequent bonding. Please refer to Figure 9. The planarization process can be chemical mechanical polishing, etc.

[0052] In some specific and preferred embodiments, the surface roughness of the planarized support layer 2 is less than 0.3 nm, the uniformity is less than 1%, and the total thickness deviation (TTV) is less than 20 μm.

[0053] Regarding step (5), a first substrate 1 is provided, and the first substrate 1 is bonded to the support layer 2; In this step, the support layer 2 is directly bonded to the support layer 2, which can bond the epitaxial wafer structure including the lower electrode layer 4, the lower acoustic reflection structure layer 71, the filler layer 9, and the support layer 2 to the first substrate 1 to form a new assembly, as shown in Figure 10. The bonding process can be a conventional process for those skilled in the art, and is not specifically limited in this invention.

[0054] Optionally, the first substrate 1 includes a substrate layer and a surface bonding layer disposed on the substrate layer. The substrate layer can be made of materials such as silicon, sapphire, silicon carbide, or diamond, and the surface bonding layer can be made of non-metallic insulating materials such as silicon or silicon dioxide.

[0055] Regarding step (6), remove the temporary substrate 8 to expose the piezoelectric layer 5; In this step, the temporary substrate 8 is removed. First, the temporary substrate 8 is thinned, and then removed by etching to expose the piezoelectric layer 5 (see Figure 11). Specifically, a mechanical thinning process can be used to thin the temporary substrate 8, controlling its thickness to be between 5 μm and 50 μm. Subsequently, a dry etching process can be used to remove the thinned temporary substrate 8 to expose the piezoelectric layer 5.

[0056] Regarding step (7), an upper acoustic reflection structure 72 and an upper electrode layer 6 are prepared on the exposed piezoelectric layer 5, such that the upper electrode layer 6 fills the interior of the upper acoustic reflection structure layer 72 and covers the surface of the upper acoustic reflection structure layer 72. This step specifically includes: (71) An upper acoustic reflection structure layer 72 is prepared on the exposed piezoelectric layer 5, such that the upper acoustic reflection structure layer 72 and the lower acoustic reflection structure layer 71 are located on both sides of the piezoelectric layer 5; For example, an upper acoustic reflection structure material is deposited on the exposed piezoelectric layer 5 to form a layer structure. Then, photoresist is applied to the surface of the layer structure. After exposure and development, the part to be etched is etched to form an upper acoustic reflection structure layer 72 with a closed-loop structure. Please refer to Figures 12 and 13.

[0057] In this step, the geometric center axes of the upper acoustic reflection structure layer 72, the lower acoustic reflection structure layer 71, and the lower electrode layer 4 overlap. The inner boundary of the lower acoustic reflection structure layer 71 is located between the inner boundary and the outer edge of the upper acoustic reflection structure layer 72, so that the projection of the lower electrode layer 4 on the plane completely covers the effective resonant region of the upper electrode layer 6. At this time, the distance between the outer edge of the upper acoustic reflection structure layer 72 and the inner edge of the lower acoustic reflection structure layer 71 is 0.5μm-3μm, and the distance between the inner edge of the upper acoustic reflection structure layer 72 and the inner edge of the lower acoustic reflection structure layer 71 is 0.5μm-3μm.

[0058] Optionally, the deposition process of the upper acoustic reflection structure layer 72 includes, but is not limited to, PVD, and the material of the upper acoustic reflection structure layer 72 is a metallic material, including but not limited to molybdenum, aluminum, and tungsten. The material of the upper acoustic reflection structure layer 72 and the material of the lower acoustic reflection structure can be the same material or different materials.

[0059] (72) An upper electrode layer 6 is prepared on the exposed piezoelectric layer 5 and upper acoustic reflection structure layer 72, such that the upper electrode layer 6 fills the interior of the upper acoustic reflection structure layer 72 and covers the surface of the upper acoustic reflection structure layer 72. For example, the upper electrode material is deposited on the exposed piezoelectric layer 5 and the upper acoustic reflection structure layer 72 to form a layer structure. Then, photoresist is applied to the surface of the layer structure. After exposure and development, the part to be etched is etched to achieve patterned etching, so that the upper electrode layer 6 fills the interior of the upper acoustic reflection structure layer 72 and is deposited on the upper acoustic reflection structure layer 72, so that the outer edge of the upper acoustic reflection structure layer 72 coincides with the outer edge of the upper electrode layer 6, forming a protruding structure at both ends, as shown in Figure 14.

[0060] In this step, the upper electrode layer 6 is positioned opposite to the lower electrode layer 4, and the geometric center axes of the upper electrode layer 6 and the lower electrode layer 4 overlap. The upper electrode layer 6 also overlaps with the geometric center axis of the upper acoustic reflection structure layer 72. At this time, the size of the upper electrode layer 6 is smaller than the size of the lower electrode layer 4 and the filling layer 9, and the lower electrode layer 4 completely covers the effective resonant region of the upper electrode layer 6. Optionally, the distance between the outer edge of the upper electrode layer 6 and the outer edge of the lower electrode layer 4 is controlled between 1 μm and 5 μm, and the distance between the outer edge of the upper electrode layer 6 and the outer edge of the filling layer 9 is controlled between 1 μm and 5 μm.

[0061] Furthermore, the thickness of the upper electrode layer 6 is 100nm-1000nm. The deposition process of the upper electrode layer 6 includes, but is not limited to, PVD, and the upper electrode material is a metallic material, including but not limited to molybdenum, aluminum, and tungsten. The upper electrode material and the lower electrode material can be the same material or different materials, and the upper electrode material and the material of the upper acoustic reflection structure layer 72 can be the same material or different materials.

[0062] Regarding step (8), remove the filling layer 9 to form a cavity 3.

[0063] In this step, the filling layer 9 is removed, and the first substrate 1, the lower electrode layer 4, and the lower acoustic reflection structure layer 71 form a cavity 3, as shown in Figures 1-3. At this time, the projection of the lower electrode layer 4 on the plane completely covers the entire area of ​​the cavity 3, and the distance between the outer edge of the lower electrode layer 4 and the sidewall of the cavity 3 is greater than 3 μm.

[0064] Alternatively, the filling layer 9 can be removed using a dry etching or wet etching process to form the resonant cavity 3.

[0065] The present invention will be further described below with reference to specific embodiments: Example 1 This embodiment provides a cavity-type bulk acoustic resonator, comprising: a first substrate, a support layer, a lower electrode layer, a piezoelectric layer, an upper electrode layer, and an acoustic reflection structure layer. The support layer is bonded to the first substrate and has a cavity formed by an indentation in its upper surface. The lower electrode layer covers the surface of the support layer above the cavity. The piezoelectric layer is disposed on the upper surface of the lower electrode layer and contacts the support layer. The acoustic reflection structure layer includes a lower acoustic reflection structure layer and an upper acoustic reflection structure layer, both of which are closed ring structures. The lower electrode layer fills the interior of the lower acoustic reflection structure layer and covers its surface. The lower electrode layer is also disposed on the outside of the lower acoustic reflection structure layer and covers part of its outer side. The upper electrode layer fills the interior of the upper acoustic reflection structure layer and covers its surface.

[0066] The lower electrode layer and the upper electrode layer are correspondingly arranged, and their geometric center axes overlap. The lower electrode layer completely covers the effective resonant area of ​​the upper electrode layer. The upper acoustic reflection structure layer overlaps with the geometric center axis of the upper electrode layer, and the lower acoustic reflection structure layer overlaps with the geometric center axis of the upper electrode layer. The inner boundary of the lower acoustic reflection structure layer is located outside the edge projection range of the effective resonant area covered by the upper electrode layer. The inner boundary of the lower acoustic reflection structure layer is located between the inner boundary and the outer edge of the upper acoustic reflection structure layer. The outer edge of the upper acoustic reflection structure layer coincides with the outer edge of the upper electrode layer. The projection of the lower electrode layer on the plane completely covers the entire area of ​​the cavity.

[0067] The distance W1 between the inner boundary of the lower acoustic reflection structure layer and the outer edge of the upper acoustic reflection structure layer is 2 μm; the distance W2 between the inner boundary of the lower acoustic reflection structure layer and the inner boundary of the upper acoustic reflection structure layer is 2 μm; the distance W3 between the outer edge of the lower acoustic reflection structure layer and the outer edge of the upper acoustic reflection structure layer is 1 μm; the distance W4 between the outer edge of the lower acoustic reflection structure layer and the outer edge of the lower electrode layer is 5 μm; and the thickness H1 of the lower acoustic reflection structure layer is 200 nm. The width W5 of the lower acoustic reflection structure layer is 2 μm, the thickness H2 of the lower electrode layer is 300 nm, the thickness H3 of the upper acoustic reflection structure layer is 250 nm, the width W6 of the upper acoustic reflection structure layer is 3 μm, the thickness H4 of the upper electrode layer is 500 nm, the distance W7 between the outer edge of the lower electrode and the sidewall of the cavity is greater than 3 μm, the distance W8 between the sidewall of the cavity and the outer edge of the lower acoustic reflection structure layer is 3 μm, and the thickness H5 of the cavity is 2.5 μm.

[0068] The material of the acoustic reflection structure layer is molybdenum.

[0069] Accordingly, this embodiment also provides a method for fabricating a cavity-type bulk acoustic resonator, comprising the following steps: (1) A temporary substrate is provided, and a piezoelectric layer is prepared on the temporary substrate; (2) A lower acoustic reflection structure layer and a lower electrode layer are prepared on the piezoelectric layer, such that the lower electrode layer fills the interior of the lower acoustic reflection structure layer and covers the lower acoustic reflection structure layer; (3) A filling layer is prepared on the lower electrode layer and the lower acoustic reflection structure layer, wherein the projection of the filling layer on the plane is completely located within the effective resonant region of the lower electrode layer; (4) A support layer is prepared on the filler layer and the piezoelectric layer not covered by the filler layer, and the support layer is planarized. (5) Provide a first substrate and bond the first substrate to the support layer; (6) Remove the temporary substrate to expose the piezoelectric layer; (7) An upper acoustic reflection structure layer and an upper electrode layer are prepared on the exposed piezoelectric layer, such that the upper electrode layer fills the interior of the upper acoustic reflection structure layer and covers the surface of the upper acoustic reflection structure layer; (8) Remove the filling layer to form a cavity.

[0070] The impedance and Q value of the cavity-type bulk acoustic resonator obtained in Example 1 were tested, and the test results are shown in Figures 15 and 16.

[0071] Figure 15 shows the impedance test results of the obtained cavity-type bulk acoustic wave resonator, and Figure 16 shows the Q value test results of the obtained cavity-type bulk acoustic wave resonator. As can be seen from the figures, based on the original epitaxial cavity-type resonator, by setting upper and lower acoustic reflection structure layers on the upper and lower electrode layers, the obtained cavity-type bulk acoustic wave resonator exhibits an impedance valley at 2.08 GHz in both modes. However, the impedance in the "ACmodify" mode significantly increases at 2.14 GHz, indicating optimized anti-resonance performance. This can suppress energy dissipation from the edge of the resonant region during resonance of the resonator and filter, further improving the Q value of the resonator based on piezoelectric thin films made of epitaxial materials such as gallium oxide.

[0072] The above description is merely a preferred embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any equivalent variations made in accordance with the claims of the present invention are still within the scope of the present invention.

Claims

1. A cavity-type bulk acoustic resonator, characterized in that, include: First substrate, A support layer is bonded to the first substrate, and the support layer has a cavity formed by an indentation in its upper surface; A lower electrode layer that covers the surface of the support layer above the cavity; A piezoelectric layer is disposed on the upper surface of the lower electrode layer and in contact with the support layer; An upper electrode layer is disposed on the upper surface of the piezoelectric layer; The acoustic reflection structure layer includes a lower acoustic reflection structure layer and an upper acoustic reflection structure layer, both of which are closed structures. The lower electrode layer fills the interior of the lower acoustic reflection structure layer and covers its surface, while the upper electrode layer fills the interior of the upper acoustic reflection structure layer and covers its surface.

2. The cavity-type bulk acoustic resonator as described in claim 1, characterized in that, The lower electrode layer and the upper electrode layer are respectively disposed, and the geometric center axes of the lower electrode layer and the upper electrode layer overlap. The lower electrode layer completely covers the effective resonant region of the upper electrode layer.

3. The cavity-type bulk acoustic resonator as described in claim 2, characterized in that, The upper acoustic reflection structure layer overlaps with the geometric center axis of the upper electrode layer, the lower acoustic reflection structure layer overlaps with the geometric center axis of the upper electrode layer, and the inner boundary of the lower acoustic reflection structure layer is located outside the edge projection range of the effective resonant area covered by the upper electrode layer.

4. The cavity-type bulk acoustic resonator as described in claim 2, characterized in that, The inner boundary of the lower acoustic reflection structure layer is located between the inner boundary and the outer edge of the upper acoustic reflection structure layer, so that the projection of the lower electrode layer on the plane completely covers the effective resonant region of the upper electrode layer.

5. The cavity-type bulk acoustic resonator as described in claim 1 or 4, characterized in that, The distance between the inner boundary of the lower acoustic reflection structure layer and the outer edge of the upper acoustic reflection structure layer is 0.5μm-3μm; The distance between the inner boundary of the lower acoustic reflection structure layer and the inner boundary of the upper acoustic reflection structure layer is 0.5μm-3μm; The distance between the outer edge of the lower acoustic reflection structure layer and the outer edge of the upper acoustic reflection structure layer is 0.5μm-2μm.

6. The cavity-type bulk acoustic resonator as described in claim 1, characterized in that, The lower electrode layer is also disposed on the outside of the lower acoustic reflection structure layer and covers part of the outer side of the lower acoustic reflection structure layer; The distance between the outer edge of the lower acoustic reflection structure layer and the outer edge of the lower electrode layer is 1μm-10μm; The thickness of the lower acoustic reflection structure layer is 10nm-500nm, and the width of the lower acoustic reflection structure layer is 0.5μm-3μm; the thickness of the lower electrode layer is 100nm-500nm.

7. The cavity-type bulk acoustic resonator as described in claim 1, characterized in that, The outer edge of the upper acoustic reflection structure layer coincides with the outer edge of the upper electrode layer; The thickness of the upper acoustic reflection structure layer is 50nm-500nm, and the width of the upper acoustic reflection structure layer is controlled between 0.5μm and 5μm. The thickness of the upper electrode layer is 100nm-1000nm.

8. The cavity-type bulk acoustic resonator as described in claim 1, characterized in that, The projection of the lower electrode layer on the plane completely covers the entire area of ​​the cavity, and the distance between the outer edge of the lower electrode layer and the sidewall of the cavity is greater than 3μm; The distance between the sidewall of the cavity and the outer edge of the lower acoustic reflection structure layer is 1μm-5μm; The thickness of the cavity is 0.5μm-5μm.

9. The cavity-type bulk acoustic resonator as described in claim 1, characterized in that, The acoustic reflection structure layer is a closed ring structure; The first substrate includes a substrate layer and a surface bonding layer disposed on the substrate layer. The substrate layer is made of one or more of silicon, sapphire, silicon carbide, and diamond. The surface bonding layer is made of at least one of silicon and silicon dioxide. The support material of the support layer is one or more of silicon and ceramic; The material of the lower electrode layer is one or more of molybdenum, aluminum, and tungsten; The piezoelectric layer is made of one or more of aluminum nitride and gallium oxide. The material of the upper electrode layer is one or more of molybdenum, aluminum, and tungsten; The material of the acoustic reflection structure layer is one or more of molybdenum, aluminum, and tungsten.

10. A method for fabricating a cavity-type bulk acoustic resonator as described in any one of claims 1-9, characterized in that, Includes the following steps: A temporary substrate is provided, and a piezoelectric layer is fabricated on the temporary substrate; A lower acoustic reflection structure layer and a lower electrode layer are fabricated on the piezoelectric layer, such that the lower electrode layer fills the interior of the lower acoustic reflection structure layer and covers the lower acoustic reflection structure layer. A filling layer is prepared on the lower electrode layer and the lower acoustic reflection structure layer, and the projection of the filling layer on the plane is completely located within the effective resonant region of the lower electrode layer. A support layer is prepared on the filler layer and the piezoelectric layer not covered by the filler layer, and then planarized. A first substrate is provided, and the first substrate is bonded to the support layer; Remove the temporary substrate to expose the piezoelectric layer; An upper acoustic reflection structure layer and an upper electrode layer are prepared on the exposed piezoelectric layer, such that the upper electrode layer fills the interior of the upper acoustic reflection structure layer and covers the surface of the upper acoustic reflection structure layer; Remove the filling layer to form a cavity.

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