Bulk acoustic wave resonator and preparation method therefor, and filter
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-11-14
- Publication Date
- 2026-08-13
Smart Images
Figure CN2025135146_13082026_PF_FP_ABST
Abstract
Description
A bulk acoustic resonator and its fabrication method, and a filter
[0001] Cross-reference to related applications
[0002] This application claims priority to Chinese Patent Application No. 2025101282075, filed on February 5, 2025, entitled "A Bulk Acoustic Resonator and a Method for its Fabrication", the entire contents of which are incorporated herein by reference. Technical Field
[0003] This application relates to the field of microelectromechanical systems (MEMS) technology, and more specifically, to a bulk acoustic resonator and its fabrication method. Background Technology
[0004] With the rapid development of wireless communication technology, more and more devices are transmitting and receiving information at higher frequency bands, placing increasingly stringent demands on radio frequency front-end circuits. Consequently, the market demand for high-performance filters is growing rapidly. Bulk acoustic wave (BAW) filters, with their high quality factor, good out-of-band rejection, and high rectangular coefficient, are gradually becoming the mainstream in the market. BAW filters are constructed by cascading multiple resonators in a specific circuit configuration. High-performance filters require high-performance resonators, which possess a high quality factor. A high quality factor allows the filter to have lower insertion loss and a steeper roll-off characteristic, resulting in superior filtering performance. Therefore, the fabrication of resonators with high stability and superior performance is crucial.
[0005] A bulk acoustic wave resonator comprises a sandwich structure consisting of a bottom electrode, a piezoelectric layer, and a top electrode. A voltage difference is created between the bottom and top electrodes to generate longitudinal acoustic waves propagating along the thickness direction within the piezoelectric layer. In practical applications, transverse acoustic waves also exist within the piezoelectric layer, propagating along its plane. When these transverse waves reach the edge of the piezoelectric layer, leakage occurs, resulting in energy loss and a decrease in the Q value. Existing technologies incorporate an air bridge at the edge of the effective resonant region of the top electrode. This reduces energy loss and improves the Q value. However, the air bridge fabrication process thins the top electrode at the sloping surfaces on both sides of the air bridge, increasing its resistance and reducing the resonator's Q value to some extent. Furthermore, the thinner areas are more prone to breakage, posing a reliability risk.
[0006] Application content
[0007] The purpose of this application is to provide a bulk acoustic wave resonator and its fabrication method, which can improve the Q value and reliability of the bulk acoustic wave resonator.
[0008] One embodiment of this application provides a bulk acoustic resonator, including a substrate and a bottom electrode, a piezoelectric layer and a top electrode sequentially disposed on the substrate. An acoustic reflection structure is formed in the substrate. The area where the projections of the bottom electrode, the piezoelectric layer, the top electrode and the acoustic reflection structure on the substrate overlap is an effective resonant region. At the edge of the effective resonant region, the top electrode bends upward to form a gap with the piezoelectric layer. A reinforcing structure is formed on the upper surface of the top electrode. The conductivity of the reinforcing structure is greater than that of the top electrode, and the projection of the reinforcing structure on the substrate is greater than or equal to the projection of the gap on the substrate.
[0009] As an feasible approach, a passivation layer is also provided on the top electrode, the reinforcing structure is provided in the same layer as the passivation layer, the top electrode spans the gap to form a pad, and the passivation layer extends to the pad.
[0010] As one feasible approach, a passivation layer is also provided on the top electrode, and the reinforcing structure is provided in the same layer as the passivation layer. The top electrode crosses the gap to form a pad, and the reinforcing structure includes a reinforcing part provided on the gap and a connecting part provided on the pad.
[0011] As an feasible approach, a passivation layer is also provided on the top electrode, and the reinforcing structure overlaps the edge of the passivation layer.
[0012] As one possible implementation, the top electrode includes an electrode portion disposed in the effective resonant region and a bridging portion disposed in the gap. The reinforcing structure and the bridging portion are made of the same material, and both are different from the electrode portion.
[0013] As one feasible approach, the top electrode is made of molybdenum, aluminum, or tungsten, and the reinforcing structure is made of silver, copper, gold, sodium, zinc, nickel, iron, platinum, tin, or lead.
[0014] Another embodiment of this application provides a method for fabricating a bulk acoustic wave resonator, comprising: providing a substrate and sequentially forming a bottom electrode and a piezoelectric layer on the substrate, wherein an acoustic reflection structure is formed within the substrate; forming a sacrificial block on the piezoelectric layer; forming a top electrode on the piezoelectric layer, the top electrode covering the sacrificial block, wherein the area where the projections of the bottom electrode, the piezoelectric layer, the top electrode, and the acoustic reflection structure on the substrate overlap is an effective resonant region, and the sacrificial block is located at the edge of the effective resonant region; forming a reinforcing structure on the upper surface of the top electrode, wherein the conductivity of the reinforcing structure is greater than the conductivity of the top electrode, and the projection of the reinforcing structure on the substrate is greater than the projection of the sacrificial block on the substrate; and releasing the sacrificial block to form a gap.
[0015] As one feasible approach, forming a reinforcement structure on the top electrode includes: forming a passivation layer on the top electrode; etching the passivation layer to form a window that overlaps with the projection of the sacrificial block onto the substrate; and forming a reinforcement structure within the window.
[0016] As one feasible approach, the reinforcement structure extends to the side of the gap away from the effective resonant region.
[0017] As an feasible approach, before forming the reinforcing structure on the top electrode, the fabrication method of the bulk acoustic resonator further includes: etching the portion of the top electrode corresponding to the sacrificial block to expose the upper surface of the sacrificial block; when forming the reinforcing structure on the top electrode, the portion of the reinforcing structure laid on the upper surface of the sacrificial block serves as a bridging portion. Attached Figure Description
[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 is a schematic diagram of one of the structures of a bulk acoustic resonator provided in an embodiment of this application;
[0020] Figure 2 is a second schematic diagram of a bulk acoustic resonator provided in an embodiment of this application;
[0021] Figure 3 is a third schematic diagram of a bulk acoustic resonator provided in an embodiment of this application;
[0022] Figure 4 is a fourth schematic diagram of a bulk acoustic resonator provided in an embodiment of this application;
[0023] Figure 5 is a flowchart of a method for fabricating a bulk acoustic resonator according to an embodiment of this application;
[0024] Figure 6 is one of the state diagrams of a method for fabricating a bulk acoustic resonator according to an embodiment of this application;
[0025] Figure 7 is a second state diagram of a method for fabricating a bulk acoustic resonator according to an embodiment of this application;
[0026] Figure 8 is a third state diagram of a method for fabricating a bulk acoustic resonator according to an embodiment of this application;
[0027] Figure 9 is a fourth state diagram of a method for fabricating a bulk acoustic resonator according to an embodiment of this application;
[0028] Figure 10 is a fifth state diagram of a method for fabricating a bulk acoustic resonator according to an embodiment of this application;
[0029] Figure 11 is a state diagram of a method for fabricating a bulk acoustic resonator according to an embodiment of this application;
[0030] Figure 12 is a state diagram (7) of a method for fabricating a bulk acoustic resonator according to an embodiment of this application.
[0031] Figure 13 is the eighth state diagram of a method for fabricating a bulk acoustic resonator according to an embodiment of this application;
[0032] Figure 14 is a state diagram of a method for fabricating a bulk acoustic resonator according to an embodiment of this application;
[0033] Figure 15 is a state diagram of a method for fabricating a bulk acoustic resonator according to an embodiment of this application.
[0034] Icons: 100-Bulk acoustic resonator; 110-Substrate; 111-Acoustic reflection structure; 120-Bottom electrode; 130-Piezoelectric layer; 140-Top electrode; 141-Electrode section; 142-Bridging section; 150-Effective resonant region; 160-Gap; 170-Reinforcement structure; 171-Reinforcement section; 172-Connection section; 180-Passivation layer; 190-Pad; 210-Sacrificial block. Embodiments of the present invention
[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. It should be noted that, in the absence of conflict, the various features in the embodiments of this application can be combined with each other, and the combined embodiments are still within the protection scope of this application.
[0036] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and therefore should not be construed as limiting this application. Furthermore, the terms "first," "second," and "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0037] In the description of this application, it should also be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a direct connection, an indirect connection through an intermediate medium, or a connection within two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.
[0038] To prevent leakage of transverse acoustic waves inside the bulk acoustic resonator, existing technologies employ an air gap structure at the edge of the effective resonant region to reflect acoustic waves propagating to the edge of the effective resonant region, thereby reducing leakage. In practical applications, the air gap causes the top electrode to bend upwards, and the top electrode is mostly formed by vapor deposition. As a result, the thickness of the top electrode is relatively thin at the inclined surface when it bends upwards, which increases the resistance of the top electrode and makes it prone to breakage at the thinner position.
[0039] This application provides a bulk acoustic wave resonator 100, as shown in Figures 1 to 4, including a substrate 110 and a bottom electrode 120, a piezoelectric layer 130, and a top electrode 140 sequentially disposed on the substrate 110. An acoustic reflection structure 111 is formed in the substrate 110. The area where the projections of the bottom electrode 120, the piezoelectric layer 130, the top electrode 140, and the acoustic reflection structure 111 on the substrate 110 overlap is an effective resonance region 150. At the edge of the effective resonance region 150, the top electrode 140 bends upward to form a gap 160 between itself and the piezoelectric layer 130. A reinforcing structure 170 is formed on the upper surface of the top electrode 140. The conductivity of the reinforcing structure 170 is greater than that of the top electrode 140, and the projection of the reinforcing structure 170 on the substrate 110 is greater than or equal to the projection of the gap 160 on the substrate 110.
[0040] The bulk acoustic wave resonator 100 of this application embodiment is used to generate resonance. Specifically, the bulk acoustic wave resonator 100 includes a substrate 110 and a bottom electrode 120, a piezoelectric layer 130 and a top electrode 140 sequentially disposed on the substrate 110. The bottom electrode 120, the piezoelectric layer 130 and the top electrode 140 are sandwich structures. When the bulk acoustic wave resonator 100 is working, different voltages are applied to the top electrode 140 and the bottom electrode 120 to form a voltage difference between the top electrode 140 and the bottom electrode 120, and an electric field is formed between the top electrode 140 and the bottom electrode 120. The piezoelectric layer 130 is located in the electric field formed by the top electrode 140 and the bottom electrode 120. Due to the piezoelectric effect of the piezoelectric layer 130, longitudinally propagating sound waves are generated in the piezoelectric layer 130.
[0041] In practical applications, sound waves propagating along the plane of the piezoelectric layer 130 will also exist in the piezoelectric layer 130. At the edge of the effective resonant region 150, the top electrode 140 bends upward to form a gap 160 between itself and the piezoelectric layer 130. The gap 160 is filled with air. The sound reflection coefficient of air is different from that of the piezoelectric layer 130, which makes a reflective interface formed at the interface between the piezoelectric layer 130 and the gap 160. When the transverse sound wave propagates to the edge of the effective resonant region 150, the reflective interface reflects the transverse sound wave, thereby avoiding the leakage of the transverse sound wave.
[0042] In this embodiment, a reinforcing structure 170 is also formed on the upper surface of the top electrode 140. The projection of the reinforcing structure 170 onto the substrate 110 is greater than or equal to the projection of the gap 160 onto the substrate 110. The reinforcing structure 170 has a certain thickness. The reinforcing structure 170 and the top electrode 140 simultaneously serve as conductive structures located above the gap 160, increasing the thickness of the conductive structure on the gap 160. Furthermore, the conductivity of the reinforcing structure 170 is greater than that of the top electrode 140, thereby reducing the resistance of the conductive structure and consequently reducing the resistance of the resonator, thus improving the Q value of the bulk acoustic wave resonator 100. In addition, the increased thickness of the conductive structure on the gap 160 reduces the risk of breakage of the conductive structure on the gap 160, improving reliability. Therefore, the bulk acoustic wave resonator 100 of this embodiment can improve both the Q value and reliability of the bulk acoustic wave resonator 100.
[0043] The specific structure of the acoustic reflection structure 111 is not limited in this application embodiment. Those skilled in the art can set it according to the actual situation. For example, it can be a cavity as shown in Figure 1. When the acoustic reflection structure 111 is a cavity, the cavity is formed between the upper surface of the substrate 110 and the lower surface of the bottom electrode 120. Specifically, the upper surface of the substrate 110 is recessed to form a cavity; it can also be a stacked structure formed by alternating high acoustic impedance and low acoustic impedance; or it can be a back-etched cavity formed by etching the lower surface of the substrate 110.
[0044] In practical applications, a buffer layer or seed layer can be provided between the substrate 110 and the bottom electrode 120 to improve the thin film quality of the piezoelectric layer 130, thereby improving the performance of the bulk acoustic wave resonator 100.
[0045] The bulk acoustic wave resonator 100 provided in this application includes a substrate 110 and a bottom electrode 120, a piezoelectric layer 130, and a top electrode 140 sequentially disposed on the substrate 110. An acoustic reflection structure 111 is formed within the substrate 110. The overlapping region of the projections of the bottom electrode 120, the piezoelectric layer 130, the top electrode 140, and the acoustic reflection structure 111 onto the substrate 110 is an effective resonant region 150. At the edge of the effective resonant region 150, the top electrode 140 bends upward to form a gap 160 with the piezoelectric layer 130. A shape is formed on the upper surface of the top electrode 140. A reinforcing structure 170 with a certain thickness is formed. The reinforcing structure 170 and the top electrode 140 are both located above the gap 160 as conductive structures, which increases the thickness of the conductive structure on the gap 160. The conductivity of the reinforcing structure 170 is greater than that of the top electrode 140, thereby reducing the resistance of the conductive structure and thus reducing the resistance of the resonator, thereby improving the Q value of the bulk acoustic wave resonator 100. Furthermore, the projection of the reinforcing structure 170 on the substrate 110 is greater than or equal to the projection of the gap 160 on the substrate 110. In addition, the increased thickness of the conductive structure on the gap 160 reduces the risk of breakage of the conductive structure on the gap 160, improving reliability. Therefore, the bulk acoustic wave resonator 100 of this embodiment can improve the Q value and reliability of the bulk acoustic wave resonator 100.
[0046] Optionally, as shown in Figure 1, a passivation layer 180 is also provided on the top electrode 140, and the reinforcing structure 170 is disposed in the same layer as the passivation layer 180. The top electrode 140 crosses the gap 160 to form a pad 190, and the passivation layer 180 extends to the pad 190.
[0047] A passivation layer 180 is provided on the top electrode 140, which isolates the top electrode 140 from the external environment and provides a certain degree of protection for the top electrode 140. The reinforcing structure 170 is disposed in the same layer as the passivation layer 180, and the passivation layer 180 extends to the pad 190, so that the reinforcing structure 170 is located only on the gap 160, minimizing the area of the reinforcing structure 170 while ensuring its reinforcing effect.
[0048] In one possible implementation of this application embodiment, as shown in FIG2, a passivation layer 180 is further provided on the top electrode 140, and the reinforcing structure 170 is disposed in the same layer as the passivation layer 180. The top electrode 140 forms a pad 190 across the gap 160. The reinforcing structure 170 includes a reinforcing portion 171 disposed on the gap 160 and a connecting portion 172 disposed on the pad 190.
[0049] The reinforcing structure 170 and the passivation layer 180 are disposed in the same layer. The top electrode 140 crosses the gap 160 to form a pad 190. The reinforcing structure 170 also crosses the gap 160 to form a connection portion 172 on the pad 190. This makes the reinforcing structure 170 include the reinforcing portion 171 on the gap 160 and the connection portion 172 on the pad 190. In this way, the contact area between the reinforcing structure 170 and the top electrode 140 is larger, which can further reduce the resistance of the top electrode 140, thereby improving the Q value of the bulk acoustic wave resonator 100.
[0050] Optionally, as shown in Figure 3, a passivation layer 180 is also provided on the top electrode 140, and the reinforcing structure 170 overlaps the edge of the passivation layer 180.
[0051] The reinforcing structure 170 is placed at the edge of the passivation layer 180, which can increase the contact area of the reinforcing structure 170 and thus improve the stability of the reinforcing structure 170.
[0052] In addition, since the reinforcing structure 170 overlaps the passivation layer 180, the passivation layer 180 and the reinforcing structure 170 form an interface in the horizontal direction. The passivation layer 180 and the reinforcing structure 170 have different acoustic reflection coefficients, forming a reflection interface at the interface. This allows for further reflection of transverse sound waves, thereby further improving the Q value of the bulk acoustic resonator 100.
[0053] In one possible implementation of this application embodiment, as shown in FIG4, the top electrode 140 includes an electrode portion 141 disposed in the effective resonant region 150 and a bridging portion 142 disposed on the gap 160. The reinforcing structure 170 and the bridging portion 142 are made of the same material and are different from the electrode portion 141.
[0054] The top electrode 140 is divided into two parts: the part located in the effective resonant region 150 and the part located in the gap 160. The two parts have different conductivity. Specifically, the top electrode 140 located in the effective resonant region 150 is an electrode part 141, and the part located in the gap 160 is a bridging part 142. The reinforcing structure 170 is made of the same material as the bridging part 142, so that the conductivity of the bridging part 142 is greater than that of the electrode part 141. In this way, the conductivity of the conductive structure located in the gap 160 is greater, thereby reducing the resistivity of the top electrode 140 and improving the Q value of the bulk acoustic resonator 100.
[0055] In addition, the reinforcing structure 170 and the bridging portion 142 are made of the same material and can be formed in the same deposition step, so that the reinforcing structure 170 and the bridging portion 142 have better integrity.
[0056] It should be noted that, in the embodiments of this application, "located on gap 160" refers to the portion located in the same vertical direction as gap 160, that is, overlapping with the projection of gap 160 on substrate 110, and does not specifically refer to being directly disposed on gap 160.
[0057] Optionally, the top electrode 140 is made of molybdenum, aluminum, or tungsten, and the reinforcing structure 170 is made of silver, copper, gold, sodium, zinc, nickel, iron, platinum, tin, or lead.
[0058] The top electrode 140 is typically made of molybdenum, aluminum, or tungsten, which is relatively inexpensive. The reinforcing structure 170 is made of silver, copper, gold, sodium, zinc, nickel, iron, platinum, tin, or lead, which has high conductivity.
[0059] In practical applications, those skilled in the art can also select appropriate materials for the top electrode 140 and the reinforcing structure 170 according to the actual situation, as long as the conductivity of the reinforcing structure 170 material is greater than that of the top electrode 140 material.
[0060] Another embodiment of this application provides a method for fabricating a bulk acoustic resonator 100, as shown in FIG5, including:
[0061] S10: As shown in Figures 6 and 7, a substrate 110 is provided, and a bottom electrode 120 and a piezoelectric layer 130 are sequentially formed on the substrate 110. An acoustic reflection structure 111 is formed in the substrate 110.
[0062] Specifically, the method for forming the bottom electrode 120 and the piezoelectric layer 130 is not limited in the embodiments of this application. For example, chemical vapor deposition, physical vapor deposition, etc. can be used.
[0063] The specific materials of the bottom electrode 120 and the piezoelectric layer 130 are not specifically limited in this embodiment. Those skilled in the art can choose according to the actual situation, as long as the bottom electrode 120 can conduct electricity and the piezoelectric layer 130 has a piezoelectric effect.
[0064] S20: As shown in Figure 7, a sacrificial block 210 is formed on the piezoelectric layer 130;
[0065] Specifically, the sacrificial block 210 can be made by depositing sacrificial material on the piezoelectric layer 130 in one layer, and then etching it using a mask, with the sacrificial block 210 reserved at the edge of the effective resonant region 150.
[0066] Alternatively, a pre-made sacrificial block 210 can be placed in a preset position.
[0067] S30: As shown in Figure 8, a top electrode 140 is formed on the piezoelectric layer 130. The top electrode 140 covers the sacrificial block 210. The area where the projections of the bottom electrode 120, the piezoelectric layer 130, the top electrode 140, and the acoustic reflection structure 111 on the substrate 110 overlap is the effective resonant region 150. The sacrificial block 210 is located at the edge of the effective resonant region 150.
[0068] Due to the presence of the sacrificial block 210, the top electrode 140 located at the sacrificial block 210 bends upward. The sacrificial block 210 is located at the edge of the effective resonant region 150, that is, the top electrode 140 bends upward at the edge of the effective resonant region 150.
[0069] S40: As shown in Figure 9, a reinforcing structure 170 is formed on the upper surface of the top electrode 140. The conductivity of the reinforcing structure 170 is greater than that of the top electrode 140, and the projection of the reinforcing structure 170 on the substrate 110 is greater than the projection of the sacrificial block 210 on the substrate 110.
[0070] When forming the reinforcing structure 170, it can be formed by first depositing a conductive material in one layer and then etching, or it can be formed by a stripping process.
[0071] S50: As shown in Figures 10 and 11, the sacrificial block 210 is released to form a gap 160.
[0072] Before releasing the sacrificial layer, the top electrode 140 needs to be patterned to bring out the bottom electrode 120, as shown in Figure 10.
[0073] The fabrication method of the bulk acoustic wave resonator 100 according to this application embodiment involves forming a reinforcing structure 170 above a gap 160. The reinforcing structure 170 and the portion of the top electrode 140 located on the gap 160 form a conductive structure, increasing the thickness of the conductive structure on the gap 160. Furthermore, the conductivity of the reinforcing structure 170 is greater than that of the top electrode 140, thereby reducing the resistance of the conductive structure and consequently reducing the resistance of the resonator, thus improving the Q value of the bulk acoustic wave resonator 100. Additionally, the increased thickness of the conductive structure on the gap 160 reduces the risk of breakage and improves reliability. Therefore, the bulk acoustic wave resonator 100 according to this application embodiment can improve both the Q value and reliability of the bulk acoustic wave resonator 100.
[0074] In one possible implementation of this application embodiment, a reinforcing structure 170 is formed on the top electrode 140, including:
[0075] S41: As shown in Figure 8, a passivation layer 180 is formed on the top electrode 140;
[0076] The passivation layer 180 is used to isolate the top electrode 140 from the external environment, and provides a certain degree of protection for the top electrode 140.
[0077] S42: As shown in Figure 8, the etched passivation layer 180 forms a window, which overlaps with the projection of the sacrificial block 210 on the substrate 110.
[0078] In this embodiment, the etched passivation layer 180 forms a window, and the passivation layer 180 can also serve as a template to realize the fabrication of the reinforcing structure 170.
[0079] S43: As shown in Figure 9, a reinforcing structure 170 is formed within the window.
[0080] The specific structure of the reinforced structure 170 has been described in detail in the introduction of the bulk acoustic resonator 100, and will not be repeated here.
[0081] Optionally, as shown in Figure 12, the reinforcing structure 170 extends to the side of the gap 160 away from the effective resonant region 150.
[0082] Specifically, the reinforcing structure 170 includes a reinforcing portion 171 disposed on the gap 160 and a connecting portion 172 disposed on the pad 190. This results in a larger contact area between the reinforcing structure 170 and the top electrode 140, which can further reduce the resistance of the top electrode 140, thereby improving the Q value of the bulk acoustic wave resonator 100.
[0083] The reinforcing structure 170 can also extend to the upper surface of the passivation layer 180, as shown in Figure 13, which can increase the contact area of the reinforcing structure 170 and thus improve the stability of the reinforcing structure 170.
[0084] In one possible embodiment of this application, before forming the reinforcing structure 170 on the top electrode 140, the fabrication method of the bulk acoustic resonator 100 further includes:
[0085] S61: As shown in Figure 14, the portion of the top electrode 140 corresponding to the sacrificial block 210 is etched to expose the upper surface of the sacrificial block 210;
[0086] S62: As shown in FIG15, when a reinforcing structure 170 is formed on the top electrode 140, the portion of the reinforcing structure 170 laid on the upper surface of the sacrificial block 210 serves as a bridging portion 142.
[0087] Thus, the top electrode 140 includes an electrode portion 141 disposed in the effective resonant region 150 and a bridging portion 142 disposed on the gap 160. The reinforcing structure 170 is made of the same material as the bridging portion 142, so that the conductivity of the bridging portion 142 is greater than that of the electrode portion 141. In this way, the conductivity of the conductive structure located on the gap 160 is greater, thereby reducing the resistivity of the top electrode 140 and improving the Q value of the bulk acoustic resonator 100.
[0088] The reinforcing structure 170 and the bridging portion 142 are made of the same material and can be formed in the same deposition step, thus the reinforcing structure 170 and the bridging portion 142 have better integrity.
[0089] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. 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. Industrial applicability
[0090] The bulk acoustic wave resonator provided in this application includes a substrate and a bottom electrode, a piezoelectric layer, and a top electrode sequentially disposed on the substrate. An acoustic reflection structure is formed within the substrate. The area where the projections of the bottom electrode, piezoelectric layer, top electrode, and acoustic reflection structure overlap on the substrate constitutes the effective resonant region. At the edge of the effective resonant region, the top electrode bends upward to form a gap with the piezoelectric layer. A reinforcing structure with a certain thickness is formed on the upper surface of the top electrode. The reinforcing structure and the top electrode simultaneously serve as conductive structures located above the gap, increasing the thickness of the conductive structure on the gap. The conductivity of the reinforcing structure is greater than that of the top electrode, thereby reducing the resistance of the conductive structure and consequently reducing the resistance of the resonator, thus improving the Q value of the bulk acoustic wave resonator. Furthermore, the projection of the reinforcing structure on the substrate is greater than or equal to the projection of the gap on the substrate. Additionally, the increased thickness of the conductive structure on the gap reduces the risk of breakage of the conductive structure on the gap, improving reliability. Therefore, the bulk acoustic wave resonator of this application embodiment can improve the Q value and reliability of the bulk acoustic wave resonator.
Claims
1. A bulk acoustic resonator, characterized in that, The device includes a substrate and a bottom electrode, a piezoelectric layer, and a top electrode sequentially disposed on the substrate. An acoustic reflection structure is formed within the substrate. The region where the projections of the bottom electrode, the piezoelectric layer, the top electrode, and the acoustic reflection structure on the substrate overlap is an effective resonant region. At the edge of the effective resonant region, the top electrode bends upward to form a gap with the piezoelectric layer. A reinforcing structure is formed on the upper surface of the top electrode. The conductivity of the reinforcing structure is greater than that of the top electrode, and the projection of the reinforcing structure on the substrate is greater than or equal to the projection of the gap on the substrate.
2. The bulk acoustic resonator according to claim 1, characterized in that, A passivation layer is also provided on the top electrode, and the reinforcing structure is disposed in the same layer as the passivation layer. The top electrode spans the gap to form a pad, and the passivation layer extends to the pad.
3. The bulk acoustic resonator according to claim 1, characterized in that, The top electrode is also provided with a passivation layer, and the reinforcing structure is provided in the same layer as the passivation layer. The top electrode spans the gap to form a pad, and the reinforcing structure includes a reinforcing part provided on the gap and a connecting part provided on the pad.
4. The bulk acoustic resonator according to claim 1, characterized in that, The top electrode is also provided with a passivation layer, and the reinforcing structure overlaps the edge of the passivation layer.
5. The bulk acoustic resonator according to claim 1, characterized in that, The top electrode includes an electrode portion disposed in the effective resonant region and a bridging portion disposed on the gap. The reinforcing structure is made of the same material as the bridging portion, and both are different from the electrode portion.
6. The bulk acoustic resonator according to any one of claims 1 to 4, characterized in that, The top electrode is made of molybdenum, aluminum, or tungsten, and the reinforcing structure is made of silver, copper, gold, sodium, zinc, nickel, iron, platinum, tin, or lead.
7. A method for fabricating a bulk acoustic resonator, characterized in that, For fabricating the bulk acoustic resonator as described in any one of claims 1-6, comprising: A substrate is provided, and a bottom electrode and a piezoelectric layer are sequentially formed on the substrate, wherein an acoustic reflection structure is formed within the substrate; A sacrificial block is formed on the piezoelectric layer; A top electrode is formed on the piezoelectric layer, and the top electrode covers the sacrificial block. The area where the projections of the bottom electrode, the piezoelectric layer, the top electrode, and the acoustic reflection structure on the substrate overlap is the effective resonant region, and the sacrificial block is located at the edge of the effective resonant region. A reinforcing structure is formed on the upper surface of the top electrode, the conductivity of the reinforcing structure is greater than the conductivity of the top electrode, and the projection of the reinforcing structure on the substrate is greater than the projection of the sacrificial block on the substrate; Release the sacrificial block to form a gap.
8. The method for fabricating a bulk acoustic resonator according to claim 7, characterized in that, The formation of a reinforcing structure on the top electrode includes: A passivation layer is formed on the top electrode; An etched passivation layer forms a window that overlaps with the projection of the sacrificial block onto the substrate. A reinforcing structure is formed within the window.
9. The method for fabricating a bulk acoustic resonator according to claim 8, characterized in that, The reinforcing structure extends to the side of the gap away from the effective resonant region.
10. The method for fabricating a bulk acoustic resonator according to claim 7, characterized in that, Before forming the reinforcing structure on the top electrode, the method further includes: The portion of the top electrode corresponding to the sacrificial block is etched to expose the upper surface of the sacrificial block; When a reinforcing structure is formed on the top electrode, the portion of the reinforcing structure laid on the upper surface of the sacrificial block serves as a bridging portion.