Bulk acoustic wave resonator and preparation method thereof

Abstract

The invention provides a bulk acoustic wave resonator and a preparation method thereof, and belongs to the technical field of resonators. The bulk acoustic wave resonator includes: a substrate having a cavity; the resonance structure is arranged on the side, where the concave cavity is located, of the substrate and is in bonding connection with the substrate through the bonding layer, orthographic projections of the bottom electrode and the top electrode on the substrate have an overlapping area, the overlapping area is located in the area where the concave cavity is located, the overlapping area comprises a pair of first edges and a plurality of second edges, the pair of first edges are parallel to each other, and the plurality of second edges are parallel to each other. The extension direction of the first edges is perpendicular to the crystal a-axis direction of the piezoelectric film and is parallel to the sound wave polarization direction of the bulk acoustic wave resonator, the piezoelectric film is provided with two through holes, and the edge of one side of each through hole coincides with the corresponding first edge. The protruding structure is located on the side, away from the piezoelectric film, of the bottom electrode and / or the top electrode and arranged along the second edge. According to the invention, the resonator with high frequency, high electromechanical coupling coefficient and low stray mode can be better realized.

Description

Technical Field

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

[0002] With the continuous development of communication technology, the performance requirements for filters are becoming increasingly stringent. Various types of filters are constantly being developed to meet performance demands under different conditions. Bulk acoustic resonators, with their high resonant frequency and large electromechanical coupling coefficient, have been widely used in the filter field.

[0003] In related technologies, a bulk acoustic wave resonator includes a substrate, a bonding layer, and a resonant structure stacked sequentially. The substrate has a cavity filled with air, and the resonant structure includes a bottom electrode, a piezoelectric thin film, and a top electrode stacked sequentially in a direction away from the substrate, with the piezoelectric thin film covering the cavity.

[0004] However, the aforementioned bulk acoustic resonators are susceptible to the effects of generated higher-order transverse modes and leakage of the main mode acoustic waves, resulting in a high number of stray modes and affecting the performance of the bulk acoustic resonators. Summary of the Invention

[0005] This application provides a bulk acoustic resonator and its fabrication method, which can better realize a resonator with high frequency, high electromechanical coupling coefficient, and low stray modes. The technical solution includes at least the following: On one hand, a bulk acoustic wave resonator is provided, comprising: a substrate having a cavity filled with air or a Bragg reflector layer; a resonant structure disposed on one side of the cavity of the substrate and bonded to the substrate via a bonding layer, the resonant structure comprising a protruding structure and a bottom electrode, a piezoelectric film, and a top electrode sequentially stacked along a direction away from the substrate, the orthogonal projections of the bottom electrode and the top electrode on the substrate having an overlapping region, the overlapping region being located inside the region where the cavity is located, the overlapping region including a pair of first edges and a plurality of second edges, the pair of first edges being parallel to each other, the extension direction of the first edges being perpendicular to the crystal a-axis direction of the piezoelectric film and parallel to the acoustic wave polarization direction of the bulk acoustic wave resonator, the piezoelectric film having two through holes, the two through holes being respectively disposed on the outer sides of the overlapping region and inside the region where the cavity is located, one side edge of each through hole coinciding with a corresponding first edge, the protruding structure being located on the side of the bottom electrode and / or the top electrode away from the piezoelectric film and disposed along the second edge, for suppressing leakage of the main mode acoustic wave.

[0006] Optionally, the thickness of the protrusion structure is less than or equal to 3 / 4 of the thickness of the bottom electrode.

[0007] Optionally, the width of the protrusion structure in the direction perpendicular to the second edge and extending inward into the overlapping region is less than or equal to 2.5% of the characteristic width of the bottom electrode, the characteristic width of the bottom electrode being calculated using the following formula: d=4×S / C Where d is the characteristic width of the bottom electrode, S is the area of ​​the overlapping region, and C is the perimeter of the overlapping region.

[0008] Optionally, the overlapping area is trapezoidal in shape, with a pair of first edges forming the upper and lower bases of the trapezoid, and the second edge forming the waist of the trapezoid.

[0009] Optionally, the through hole is a rectangular through hole, and in the length direction parallel to the bottom edge of the trapezoid, the length of the rectangular through hole whose edge coincides with the upper base of the trapezoid is less than the length of the rectangular through hole whose edge coincides with the lower base of the trapezoid.

[0010] Optionally, the cavity is filled with air, and the bonding layer is disposed between the substrate and the piezoelectric film and located outside the region where the cavity is located.

[0011] Optionally, the cavity is filled with a Bragg reflective layer, and the bonding layer is disposed between the substrate and the piezoelectric film, and between the Bragg reflective layer and the bottom electrode.

[0012] Optionally, the bulk acoustic resonator further includes a first lead-out electrode and a second lead-out electrode, the first lead-out electrode and the second lead-out electrode being disposed on the side of the piezoelectric film away from the substrate and located outside the overlapping region, the first lead-out electrode penetrating the piezoelectric film and connected to the bottom electrode, and the second lead-out electrode being connected to the top electrode.

[0013] Optionally, the material of the piezoelectric thin film includes at least one of lithium niobate, lithium tantalate, and single-crystal aluminum nitride.

[0014] On the other hand, a method for fabricating a bulk acoustic wave resonator is provided, comprising: providing a substrate having a cavity filled with air or a Bragg reflector layer; bonding a resonant structure to the substrate via a bonding layer on one side of the cavity, the resonant structure comprising a raised structure and a bottom electrode, a piezoelectric film, and a top electrode sequentially stacked along a direction away from the substrate, the orthogonal projections of the bottom electrode and the top electrode on the substrate having an overlapping region, the overlapping region being located inside the region where the cavity is located, the overlapping region comprising a pair of first edges and a plurality of second edges, the pair of first edges being parallel to each other, the extension direction of the first edges being perpendicular to the crystal a-axis direction of the piezoelectric film and parallel to the acoustic wave polarization direction of the bulk acoustic wave resonator, the piezoelectric film having two through holes, the two through holes being respectively disposed on the outer sides of the overlapping region and inside the region where the cavity is located, one side edge of each through hole coinciding with a corresponding first edge, the raised structure being located on the side of the bottom electrode and / or the top electrode away from the piezoelectric film and disposed along the second edge, for suppressing leakage of the main mode acoustic wave.

[0015] The beneficial effects of the technical solution provided in this application include at least the following: In this embodiment, an acoustic wave reflection boundary is formed by filling the cavity of the substrate with air or a Bragg reflective layer. The orthogonal projections of the bottom electrode and the top electrode on the substrate have an overlapping region, which is located inside the region where the cavity is located. The overlapping region includes a pair of first edges and multiple second edges. The pair of first edges are parallel to each other, and the extension direction of the first edges is perpendicular to the crystal a-axis direction of the piezoelectric film and parallel to the acoustic wave polarization direction of the bulk acoustic resonator. The piezoelectric film has two through holes, which are respectively disposed on the outer sides of the overlapping region and located inside the region where the cavity is located. One edge of each through hole coincides with a corresponding first edge. The two through holes can provide a free boundary for the edges of the shear bulk acoustic waves excited in the piezoelectric film perpendicular to the polarization direction. This can change the dispersion characteristics of the acoustic waves when propagating and reflecting along this direction, suppress the generation of higher-order transverse modes propagating along this direction, reflect the main mode acoustic waves, and suppress the leakage of the main mode acoustic waves, thereby improving the mechanical quality factor of the bulk acoustic resonator. In addition, when the cavity of the substrate is filled with air, the through holes can also balance the pressure inside and outside the cavity, which is beneficial for suppressing stray modes.

[0016] By incorporating a protruding structure located on the side of the bottom electrode and / or top electrode away from the piezoelectric film and along the second edge, a low-velocity sound region can be provided for transversely propagating acoustic waves at the edge parallel to the polarization direction. Utilizing the acoustic impedance discontinuity in the propagation direction, standing waves generated by higher-order transverse modes are suppressed. Simultaneously, the reflection characteristics resulting from boundary blocking mismatch can further suppress leakage of the main mode acoustic waves, improving the mechanical quality factor of the bulk acoustic resonator. The bulk acoustic resonator of this application can better achieve high operating frequency, high electromechanical coupling coefficient, and low stray modes. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a schematic diagram of the structure of a bulk acoustic resonator provided in an embodiment of this application; Figure 2 This is a top view of a bulk acoustic resonator provided in an embodiment of this application; Figure 3 This is a simulation admittance curve of a bulk acoustic resonator provided in an embodiment of this application; Figure 4 This is a schematic diagram of another bulk acoustic resonator provided in an embodiment of this application; Figure 5 This is a schematic diagram of another type of bulk acoustic resonator provided in the embodiments of this application; Figure 6 This is a flowchart illustrating a method for fabricating a bulk acoustic resonator according to an embodiment of this application; Figures 7 to 14 This is a schematic diagram of the fabrication process of the bulk acoustic resonator in Example 1; Figure 15 This is a schematic diagram of a mesh bonding pattern provided in an embodiment of this application; Figures 16 to 23 This is a schematic diagram of the fabrication process of the bulk acoustic resonator in Example 3.

[0019] Figure label: 10: Substrate; 11: Cavity; 12: Bragg reflector layer; 121: First acoustic impedance layer; 122: Second acoustic impedance layer; 20: Bonding layer; 21: First bonded sublayer; 211: Mesh bonding region; 212: Edge bonding region; 213: Bonding groove; 214: Bonding unit; 22: Second bonded sublayer; 30: Bottom electrode; 31: Piezoelectric film; 31': Piezoelectric film material; 311: Through-hole; 32: Top electrode; 33: Damaged layer; 34: Supporting substrate; 40: Overlapping region; 41: First edge; 42: Second edge; 50: Protrusion structure; 60: First lead electrode; 61: Second lead electrode. Detailed Implementation

[0020] Unless otherwise defined, the technical or scientific terms used herein shall have the ordinary meaning understood by one of ordinary skill in the art to which this application pertains. The terms “first,” “second,” “third,” and similar terms used in this patent application specification and claims do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Similarly, the terms “an” or “a” and similar terms do not indicate a quantity limitation, but rather indicate the presence of at least one. The terms “comprising” or “including” and similar terms mean that the element or object preceding “comprising” or “including” encompasses the element or object listed following “comprising” or “including” and its equivalents, and do not exclude other elements or objects. The terms “connected” or “linked” and similar terms are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. “Up,” “down,” “left,” “right,” etc., are used only to indicate relative positional relationships, and these relative positional relationships may change accordingly when the absolute position of the described object changes. A and / or B indicates the presence of three cases: A, B, and A and B.

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application will be described in further detail below with reference to the accompanying drawings.

[0022] Example 1: Figure 1 This is a schematic diagram of the structure of a bulk acoustic resonator provided in an embodiment of this application. Figure 2 This is a top view of a bulk acoustic resonator provided in an embodiment of this application. Figure 1 It can represent Figure 2 A schematic diagram of the cross-sectional structure at section line AA. (See also...) Figure 1 and Figure 2The bulk acoustic wave resonator includes: a substrate 10 having a cavity 11 filled with air or a Bragg reflector layer; and a resonant structure disposed on one side of the substrate 10 where the cavity 11 is located and bonded to the substrate 10 via a bonding layer 20. The resonant structure includes a protrusion structure 50 and a bottom electrode 30, a piezoelectric film 31, and a top electrode 32 sequentially stacked in a direction away from the substrate 10. The orthogonal projections of the bottom electrode 30 and the top electrode 32 onto the substrate 10 have an overlapping region 40 located inside the region where the cavity 11 is located. The overlapping region 40 includes a pair of first edges 41 and a plurality of second edges 41. Edge 42, a pair of first edges 41 are parallel to each other, the extension direction of the first edges 41 is perpendicular to the crystal a-axis direction of the piezoelectric film 31 and parallel to the sound wave polarization direction of the bulk acoustic resonator, the piezoelectric film 31 has two through holes 311, the two through holes 311 are respectively disposed on the outer sides of the overlapping region 40 and located inside the region where the cavity 11 is located, one side edge of each through hole 311 coincides with a corresponding first edge 41, the protrusion structure 50 is located on the side of the bottom electrode 30 and / or the top electrode 32 away from the piezoelectric film 31 and is disposed along the second edge 42, used to suppress the leakage of the main mode acoustic wave.

[0023] In this embodiment, by filling the cavity 11 of the substrate 10 with air or a Bragg reflective layer, an acoustic wave reflection boundary is formed. The orthogonal projections of the bottom electrode 30 and the top electrode 32 on the substrate 10 have an overlapping region 40. The overlapping region 40 is located inside the region where the cavity 11 is located. The overlapping region 40 includes a pair of first edges 41 and a plurality of second edges 42. The pair of first edges 41 are parallel to each other. The extending direction of the first edges 41 is perpendicular to the crystal a-axis direction of the piezoelectric film 31 and parallel to the acoustic wave polarization direction of the bulk acoustic resonator. The piezoelectric film 31 has two through holes 3. 11. Two through holes 311 are respectively disposed on the outer sides of the overlapping region 40 and located inside the region where the cavity 11 is located. One edge of each through hole 311 coincides with a corresponding first edge 41. The two through holes 311 can provide free boundaries for the edges of the shear bulk acoustic waves excited in the piezoelectric film 31 perpendicular to the polarization direction. This can change the dispersion characteristics of the acoustic waves when they propagate and reflect along this direction, suppress the generation of higher-order transverse modes propagating along this direction, reflect the main mode acoustic waves, and suppress the leakage of the main mode acoustic waves, thereby improving the mechanical quality factor of the bulk acoustic resonator. In addition, when the cavity 11 of the substrate 10 is filled with air, the through holes 311 can also balance the pressure inside and outside the cavity 11, which is beneficial for suppressing stray modes.

[0024] By providing a protruding structure 50, located on the side of the bottom electrode 30 and / or the top electrode 32 away from the piezoelectric film 31 and along the second edge 42, a low sound velocity region can be provided for the transversely propagating sound wave at the edge parallel to the polarization direction. Utilizing the acoustic impedance discontinuity in the propagation direction, standing waves generated by higher-order transverse modes are suppressed. Simultaneously, by utilizing the reflection characteristics caused by boundary blocking mismatch, leakage of the main mode sound wave can be further suppressed, improving the mechanical quality factor of the bulk acoustic resonator. The bulk acoustic resonator of this application can better achieve high operating frequency, high electromechanical coupling coefficient, and low stray modes.

[0025] For example, the material of the substrate 10 includes one of silicon, silicon carbide, sapphire, and glass.

[0026] Optionally, the depth of the cavity 11 is from 1 μm to 10 μm.

[0027] In this embodiment, the cavity 11 is filled with air, and the bonding layer 20 is disposed between the substrate 10 and the piezoelectric film 31 and located outside the region where the cavity 11 is located.

[0028] Optionally, the bonding layer 20 may be made of at least one of gold, copper, aluminum, silicon dioxide, and benzocyclobutene (BCB).

[0029] Optionally, the material of the piezoelectric thin film 31 includes at least one of lithium niobate, lithium tantalate, and single-crystal aluminum nitride. For example, the material of the piezoelectric thin film 31 includes one or a homogeneous or heterogeneous film of lithium niobate, lithium tantalate, and single-crystal aluminum nitride.

[0030] For example, the piezoelectric film 31 is made of a material with an Euler angle of 150° to 180°. For instance, the material of the piezoelectric film 31 can be lithium YX-cut niobate (corresponding to Euler angles of [0°, -90° to -60°, 0°]).

[0031] Optionally, the materials of the bottom electrode 30 and the top electrode 32 include at least one of aluminum, molybdenum, titanium, copper, chromium, and gold. For example, the materials of the bottom electrode 30 and the top electrode 32 can be elemental aluminum, molybdenum, titanium, copper, chromium, or gold, or their alloys or multilayer thin films.

[0032] For example, the bottom electrode 30 and the top electrode 32 may be made of the same or different materials. In this embodiment, the bottom electrode 30 and the top electrode 32 are made of the same material.

[0033] For example, the overlapping region 40 is trapezoidal in shape, with a pair of first edges 41 forming the upper and lower bases of the trapezoid, and a second edge 42 forming the waist of the trapezoid. In this way, the through-hole 311 located at the first edge 41 and the protrusion structure 50 provided along the second edge 42 can better suppress stray modes, which is beneficial to improving the performance of the bulk acoustic resonator.

[0034] In other embodiments, the shape of the overlapping region 40 can also be a rectangle or other polygons, as long as the extension direction of the first edge 41 is perpendicular to the crystal a-axis direction of the piezoelectric film 31 and parallel to the acoustic wave polarization direction of the bulk acoustic resonator. This application does not impose any restrictions on this.

[0035] Optionally, the bulk acoustic wave resonator further includes a first lead-out electrode 60 and a second lead-out electrode 61. The first lead-out electrode 60 and the second lead-out electrode 61 are disposed on the side of the piezoelectric film 31 away from the substrate 10 and outside the overlapping region 40. The first lead-out electrode 60 penetrates the piezoelectric film 31 and is connected to the bottom electrode 30, and the second lead-out electrode 61 is connected to the top electrode 32. By setting the first lead-out electrode 60 and the second lead-out electrode 61, they can serve as electrode connection lines to facilitate the connection of the bottom electrode 30 and the bottom electrode 32 with external electrical signals.

[0036] For example, the connection point between the first lead electrode 60 and the bottom electrode 30 is located in the region where the cavity 11 is situated and is spaced apart from the bonding layer 20. This prevents short circuits when the bonding layer 20 is made of a metallic material.

[0037] For example, the through hole 311 is a rectangular through hole 311. In the length direction parallel to the bottom edge of the trapezoid, the length of the rectangular through hole 311 whose edge coincides with the upper bottom of the trapezoid is less than the length of the rectangular through hole 311 whose edge coincides with the lower bottom of the trapezoid.

[0038] Optionally, the thickness of the protrusion structure 50 is less than or equal to 3 / 4 of the thickness of the bottom electrode 30.

[0039] Optionally, the width of the protrusion 50 in the direction perpendicular to the second edge 42 and extending into the overlapping region 40 is less than or equal to 2.5% of the characteristic width of the bottom electrode 30. The characteristic width of the bottom electrode 30 is calculated using the following formula (1): d = 4 × S / C (1) Where d is the characteristic width of the bottom electrode 30, S is the area of ​​the overlapping region 40, and C is the perimeter of the overlapping region 40.

[0040] The thickness and width of the protrusion structure 50 are within the above range, which can better suppress the leakage of the main mode acoustic wave and help improve the mechanical quality factor of the device.

[0041] Optionally, the material of the protrusion structure 50 is the same as the material of the bottom electrode 30. In other embodiments, the material of the protrusion structure 50 may also be different from the material of the bottom electrode 30. For example, the material of the protrusion structure 50 may also be a metal or its compound with a high density and Young's modulus, such as tungsten. This application does not limit this.

[0042] It should be noted that in this embodiment, the protrusion structure 50 is located on the side of the bottom electrode 30 away from the piezoelectric film 31. In other embodiments, the protrusion structure 50 may be located on both the side of the bottom electrode 30 away from the piezoelectric film 31 and the side of the top electrode 32 away from the piezoelectric film 31; or the protrusion structure 50 may be located only on the side of the top electrode 32 away from the piezoelectric film 31.

[0043] Figure 3 This is a simulated admittance curve of a bulk acoustic resonator provided in an embodiment of this application. Figure 3 As shown, the bulk acoustic resonator of this application can effectively suppress stray modes other than the main resonant mode, reduce the interference of stray modes on the main resonant mode, and has a high quality factor.

[0044] Example 2: Figure 4 This is a schematic diagram of another bulk acoustic resonator provided in an embodiment of this application. Figure 4 As shown, the only difference between this embodiment and Embodiment 1 is the way the protruding structure 50 is set.

[0045] In this embodiment, the protrusion structure 50 is located on the side of the bottom electrode 30 and the top electrode 32 away from the piezoelectric film 31 and is disposed along the second edge 42.

[0046] Optionally, the materials of the protrusion 50 located under the bottom electrode 30 and the protrusion 50 located on the top electrode 32 may be the same or different; the thicknesses of the protrusion 50 located under the bottom electrode 30 and the protrusion 50 located on the top electrode 32 may be the same or different.

[0047] Example 3: Figure 5 This is a schematic diagram of another type of bulk acoustic resonator provided in an embodiment of this application. For example... Figure 5 As shown, the difference between this embodiment and embodiment 1 lies in the different medium filling the cavity 1, the different bonding layer 20, and the different ways of setting the protrusion structure 50.

[0048] In this embodiment, the cavity 11 is filled with a Bragg reflective layer 12, and the bonding layer 20 is disposed between the substrate 10 and the piezoelectric film 31, and between the Bragg reflective layer 12 and the bottom electrode 30.

[0049] Optionally, the Bragg reflector layer 12 includes multiple alternately stacked first acoustic impedance layers 121 and second acoustic impedance layers 122. The acoustic impedance of the first acoustic impedance layer 121 is less than that of the second acoustic impedance layer 122. The second acoustic impedance layer 122 is the part of the Bragg reflector layer 12 that is in contact with the bonding layer 20. By setting the Bragg reflector layer 12, sound waves can be reflected, sound wave leakage from the substrate 10 can be suppressed, and the reliability of the bulk acoustic resonator under mechanical shock and high-power signal input can be improved.

[0050] It should be noted that the acoustic impedance of the material can be calculated using the following formula (2): Z = ρ × v (2) Where Z is the acoustic impedance of the material, ρ is the density of the material, and v is the phase velocity of the acoustic wave mode used by the resonator propagating in the material.

[0051] For example, the material of the first acoustic impedance layer 121 can be a material with low acoustic impedance such as silicon dioxide, silicon nitride, polydimethylsiloxane, or BCB.

[0052] For example, the material of the second acoustic impedance layer 122 can be a material with high acoustic impedance such as tungsten, molybdenum, chromium, or hafnium dioxide.

[0053] For example, the ratio of the acoustic impedance of the second acoustic impedance layer 122 to the acoustic impedance of the first acoustic impedance layer 121 is greater than or equal to 2.5.

[0054] In this embodiment, the material of the bonding layer 20 can be the same as the material of the first acoustic impedance layer 121.

[0055] For example, the thickness of the bonding layer 20 can be determined according to the following formula (3): d=v×(2n-1) / (4×f)(3) Where d is the thickness of the bonding layer 20, v is the phase velocity of the acoustic wave mode used by the resonator propagating in the material, f is the average value of the resonant point and anti-resonant point of the resonator, or the center frequency of the filter passband, and n can be 1, 2 or 3.

[0056] In this embodiment, the protrusion structure 50 is located only on the side of the top electrode 32 away from the piezoelectric film 31 and is disposed along the second edge 42.

[0057] Figure 6 This is a flowchart illustrating a method for fabricating a bulk acoustic resonator according to an embodiment of this application. Figure 6 As shown, the preparation method includes: In step S1001, a substrate is provided.

[0058] The substrate has a cavity filled with air or a Bragg reflective layer.

[0059] In step S1002, the resonant structure is bonded to the substrate on one side of the cavity of the substrate through a bonding layer.

[0060] The resonant structure includes a raised structure and a bottom electrode, a piezoelectric film, and a top electrode stacked sequentially along a direction away from the substrate. The orthogonal projections of the bottom electrode and the top electrode onto the substrate have an overlapping region located inside the cavity. The overlapping region includes a pair of first edges and multiple second edges. The pair of first edges are parallel to each other, and the extension direction of the first edges is perpendicular to the crystal a-axis direction of the piezoelectric film and parallel to the acoustic wave polarization direction of the bulk acoustic resonator. The piezoelectric film has two through holes, which are respectively disposed on the outer sides of the overlapping region and inside the cavity. One edge of each through hole coincides with a corresponding first edge. The raised structure is located on the side of the bottom electrode and / or the top electrode away from the piezoelectric film and is disposed along the second edge to suppress the leakage of the main mode acoustic wave.

[0061] It should be noted that the preparation method embodiments are based on the same inventive concept as the above embodiments 1 to 3. The beneficial effects of the embodiments of this disclosure can be found in the above embodiments 1 to 3, and will not be repeated here.

[0062] Figures 7 to 14 This is a schematic diagram illustrating the fabrication process of the bulk acoustic resonator in Example 1. See also... Figure 1 and Figure 2 as well as Figures 7 to 14 The fabrication method of this bulk acoustic resonator may include the following steps: First step, such as Figure 7 As shown, a substrate 10 is provided.

[0063] For example, a first wafer can be provided, and the first wafer can be etched by photolithography and etching techniques to obtain a substrate 10 with a cavity 11.

[0064] The second step, as Figure 8 As shown, a first bonding layer 21 is formed on the substrate 10.

[0065] Figure 15 This is a schematic diagram of a mesh bonding pattern provided in an embodiment of this application. Figure 8 and Figure 15As shown, during the formation of the first bonded sublayer 21, a grid bonding pattern can be formed on the wafer. The grid bonding pattern includes a grid bonding region 211 and an edge bonding region 212, with the edge bonding region 212 located around the grid bonding region 211. The grid bonding region 211 includes multiple bonding units 214 arranged in an array and bonding grooves 213 located between each bonding unit 214. Each bonding unit 214 has multiple cavities 11. That is, each bonding unit 214 can subsequently be used to form multiple bulk acoustic resonators through dicing and splitting.

[0066] For example, the cavities 11 in each bonding unit 214 can be arranged equidistantly or unequally. By meshing the bonding pattern during the bonding process, flow space can be provided for the bonding material. During the bonding process, the bonding material uses its fluidity to fill the bonding grooves 213, i.e., the mesh gaps, expelling gas from the bonding interface, avoiding the formation of voids, releasing thermal stress during the bonding process, reducing slippage of the bonded wafer, and ensuring bonding alignment accuracy. This achieves high-quality, high-uniformity bonding and reduces material costs. Furthermore, meshed bonding can reduce the requirements for global flatness, improve the success rate and strength of initial bonding, and suppress stress accumulation and transmission, preventing wafer warpage and device performance drift.

[0067] It should be noted that when forming the first bonded sublayer 21, the bonding material located in the cavity 11 can be retained, which can simplify the process steps, and the bonding material in the cavity 11 will not have a significant impact on the performance of the bulk acoustic resonator.

[0068] The third step, as Figure 9 As shown, a piezoelectric-on-insulator (POI) wafer is provided.

[0069] For example, the POI wafer includes a support substrate 34, a damage layer 33 and a piezoelectric thin film material 31' stacked sequentially.

[0070] Step four, as Figure 10 As shown, a bottom electrode 30 and a bump structure 50 are formed on the POI wafer.

[0071] Step 5, as Figure 11 As shown, a second bonding layer 22 is formed on the piezoelectric thin film material 31'.

[0072] For example, the bonding pattern of the second bonding sublayer 22 is the same as that of the first bonding sublayer 21 except for the region where the cavity 11 is located.

[0073] Step 6, as follows Figure 11 and Figure 12As shown, a through hole 311 is formed by etching the piezoelectric thin film material 31'.

[0074] For example, the piezoelectric thin film material 31' can be etched using photolithography and etching techniques, with the etching depth just penetrating the piezoelectric thin film material 31' or etching into the damaged layer 33.

[0075] Step 7, as Figure 13 As shown, the first bonding sublayer 21 is bonded to the second bonding sublayer 22.

[0076] For example, this step can be gold-gold bonding, silicon dioxide-silicon dioxide bonding, aluminum-copper bonding, or BCB bonding, etc.

[0077] Step 8, as Figure 14 As shown, the damaged layer 33 and the supporting substrate 34 are removed.

[0078] Step 9, as Figure 1 As shown, a top electrode 32 is formed on the piezoelectric thin film 31.

[0079] Figures 16 to 23 This is a schematic diagram illustrating the fabrication process of the bulk acoustic resonator in Example 3. See also... Figure 5 as well as Figures 16 to 23 The fabrication method of this bulk acoustic resonator may include the following steps: First step, such as Figure 16 As shown, a substrate 10 is provided.

[0080] For example, a first wafer can be provided, and the first wafer can be etched by photolithography and etching techniques to obtain a substrate 10 with a cavity 11.

[0081] The second step, as Figure 17 As shown, a Bragg reflector layer 12 is formed in the cavity 11.

[0082] For example, a plurality of alternating layers of first acoustic impedance layer 121 and second acoustic impedance layer 122 can be formed in the cavity 11 by photolithography and deposition processes to obtain Bragg reflector layer 12.

[0083] The third step, as Figure 18 As shown, a first bonding layer 21 is formed on the substrate 10.

[0084] Step four, as Figure 19 As shown, a POI wafer is provided.

[0085] For example, the POI wafer includes a support substrate 34, a damage layer 33 and a piezoelectric thin film material 31' stacked sequentially.

[0086] Step 5, as Figure 20As shown, a bottom electrode 30 is formed on the POI wafer.

[0087] Step 6, as follows Figure 21 As shown, a second bonding layer 22 is formed on the piezoelectric thin film material 31' and the bottom electrode 30.

[0088] For example, a second bonding layer 22 can be formed on the piezoelectric thin film material 31' and the bottom electrode 30 by a deposition process and a planarization process.

[0089] Step 7, as Figure 22 As shown, the first bonding sublayer 21 is bonded to the second bonding sublayer 22.

[0090] For example, this step can be silicon dioxide-silicon dioxide bonding.

[0091] Step 8, as Figure 23 As shown, the damaged layer 33 and the supporting substrate 34 are removed.

[0092] Step 9, as Figure 23 and Figure 5 As shown, the piezoelectric thin film material 31' is etched to form a through hole 311, and a top electrode 32 and a protrusion structure 50 are formed on the piezoelectric thin film 31.

[0093] It should be noted that the above Figures 7 to 23 In the preparation method examples, the markings on each film material only indicate... Figure 1 or Figure 5 The corresponding membrane structure states during the fabrication process, and the shape, material, positional relationship, and size of each membrane layer in the final bulk acoustic resonator can be found in [reference needed]. Figure 1 and Figure 5 Detailed descriptions of related structural embodiments are omitted here.

[0094] The above description is merely an optional embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A bulk acoustic resonator, characterized in that, include: A substrate having a cavity filled with air or a Bragg reflective layer; A resonant structure is disposed on one side of the cavity of the substrate and bonded to the substrate via a bonding layer. The resonant structure includes a raised structure and a bottom electrode, a piezoelectric film, and a top electrode stacked sequentially in a direction away from the substrate. The orthogonal projections of the bottom electrode and the top electrode on the substrate have an overlapping region. The overlapping region is located inside the region where the cavity is located. The overlapping region includes a pair of first edges and a plurality of second edges. The pair of first edges are parallel to each other. The extension direction of the first edges is perpendicular to the crystal a-axis direction of the piezoelectric film and parallel to the acoustic wave polarization direction of the bulk acoustic resonator. The piezoelectric film has two through holes, which are respectively disposed on the outer sides of the overlapping region and inside the region where the cavity is located. One edge of each through hole coincides with a corresponding first edge. The raised structure is located on the side of the bottom electrode and / or the top electrode away from the piezoelectric film and is disposed along the second edge to suppress the leakage of the main mode acoustic wave.

2. The bulk acoustic resonator according to claim 1, characterized in that, The thickness of the protrusion structure is less than or equal to 3 / 4 of the thickness of the bottom electrode.

3. The bulk acoustic resonator according to claim 1, characterized in that, The width of the protrusion structure in the direction perpendicular to the second edge and extending inward into the overlapping region is less than or equal to 2.5% of the characteristic width of the bottom electrode, and the characteristic width of the bottom electrode is calculated using the following formula: d=4×S / C Where d is the characteristic width of the bottom electrode, S is the area of ​​the overlapping region, and C is the perimeter of the overlapping region.

4. The bulk acoustic resonator according to any one of claims 1 to 3, characterized in that, The overlapping area is trapezoidal in shape, with the first edge being the upper and lower bases of the trapezoid, and the second edge being the waist of the trapezoid.

5. The bulk acoustic resonator according to claim 4, characterized in that, The through hole is a rectangular through hole. In the length direction parallel to the bottom edge of the trapezoid, the length of the rectangular through hole whose edge coincides with the upper base of the trapezoid is less than the length of the rectangular through hole whose edge coincides with the lower base of the trapezoid.

6. The bulk acoustic resonator according to any one of claims 1 to 3 or claim 5, characterized in that, The cavity is filled with air, and the bonding layer is disposed between the substrate and the piezoelectric film and located outside the region where the cavity is located.

7. The bulk acoustic resonator according to any one of claims 1 to 3 or claim 5, characterized in that, The cavity is filled with a Bragg reflective layer, and the bonding layer is disposed between the substrate and the piezoelectric film, and between the Bragg reflective layer and the bottom electrode.

8. The bulk acoustic resonator according to any one of claims 1 to 3 or claim 5, characterized in that, The bulk acoustic wave resonator further includes a first lead-out electrode and a second lead-out electrode. The first lead-out electrode and the second lead-out electrode are disposed on the side of the piezoelectric film away from the substrate and outside the overlapping region. The first lead-out electrode passes through the piezoelectric film and is connected to the bottom electrode, and the second lead-out electrode is connected to the top electrode.

9. The bulk acoustic resonator according to any one of claims 1 to 3 or claim 5, characterized in that, The piezoelectric thin film is made of at least one of lithium niobate, lithium tantalate, and single-crystal aluminum nitride.

10. A method for fabricating a bulk acoustic resonator, characterized in that, include: A substrate is provided having a cavity filled with air or a Bragg reflective layer; A resonant structure is bonded to the substrate via a bonding layer on one side of the cavity in the substrate. The resonant structure includes a raised structure and a bottom electrode, a piezoelectric film, and a top electrode stacked sequentially in a direction away from the substrate. The orthogonal projections of the bottom electrode and the top electrode on the substrate have an overlapping region, which is located inside the region where the cavity is located. The overlapping region includes a pair of first edges and a plurality of second edges. The pair of first edges are parallel to each other, and the extension direction of the first edges is perpendicular to the crystal a-axis direction of the piezoelectric film and parallel to the acoustic wave polarization direction of the bulk acoustic resonator. The piezoelectric film has two through holes, which are respectively disposed on the outer sides of the overlapping region and inside the region where the cavity is located. One edge of each through hole coincides with a corresponding first edge. The raised structure is located on the side of the bottom electrode and / or the top electrode away from the piezoelectric film and is disposed along the second edge to suppress the leakage of the main mode acoustic wave.

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