A bulk acoustic wave resonator and a method for manufacturing the same

Abstract

The present application discloses a bulk acoustic wave resonator and a method for preparing the same, relating to the field of microelectromechanical systems. The bulk acoustic wave resonator of the present application comprises a substrate and a bottom electrode, a piezoelectric layer, and a top electrode sequentially arranged 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 overlap on the substrate constitutes an effective resonance region. At the edge of the effective resonance region, the top electrode bends upward to form a gap between the top electrode and the piezoelectric layer. A reinforcement structure is formed on the upper surface of the top electrode. The conductivity of the reinforcement structure is greater than that of the top electrode, and the projection of the reinforcement structure on the substrate is greater than or equal to the projection of the gap on the substrate. The bulk acoustic wave resonator and its preparation method provided by the present application can improve the Q value and reliability of the bulk acoustic wave resonator.

Description

Technical Field

[0001] The present application relates to the technical field of micro-electromechanical systems, and in particular to a bulk acoustic wave resonator and a method for preparing the same. Background Art

[0002] With the rapid development of wireless communication technology, more and more devices are transmitting and receiving information at higher frequencies, placing increasingly stringent demands on RF front-end circuits. Consequently, the market demand for high-performance filters is growing. Bulk acoustic wave filters, with their high quality factor, excellent out-of-band suppression, and high rectangular coefficient, are gradually becoming mainstream in the market. Bulk acoustic wave filters are composed of multiple resonators cascaded in a specific circuit. High-performance filters require high-performance resonators, which have a high quality factor. This high quality factor enables the filter to have lower insertion loss and a steeper roll-off characteristic, resulting in superior filtering performance. Therefore, it is crucial to produce resonators with high stability and superior performance.

[0003] A bulk acoustic wave resonator comprises a sandwich structure formed by a bottom electrode, a piezoelectric layer, and a top electrode. A voltage difference is formed between the bottom and top electrodes to generate a longitudinal acoustic wave that propagates in the thickness direction of the piezoelectric layer. In actual applications, the piezoelectric layer also contains transverse acoustic waves that propagate along the plane where the piezoelectric layer is located. When the transverse acoustic waves propagate to the edge of the piezoelectric layer, they leak out, causing energy loss and thus reducing the Q value. In the prior art, an air bridge is formed at the edge of the effective resonance region of the top electrode to reduce energy loss and improve the Q value. However, during the air bridge fabrication process, the thickness of the top electrode becomes thinner at the inclined surfaces on both sides of the air bridge, which increases the resistance of the top electrode and reduces the Q value of the resonator to a certain extent. Moreover, the thinner locations are prone to fracture, which increases the reliability risk. Summary of the Invention

[0004] The purpose of this application is to provide a bulk acoustic wave resonator and a preparation method thereof, which can improve the Q value and reliability of the bulk acoustic wave resonator.

[0005] On the one hand, an embodiment of the present application provides a bulk acoustic wave resonator, including a substrate and a bottom electrode, a piezoelectric layer and a top electrode arranged in sequence on the substrate, an acoustic reflection structure is formed in the substrate, and the area where the projections of the bottom electrode, the piezoelectric layer, the top electrode and the acoustic reflection structure overlap on the substrate is an effective resonance area. At the edge of the effective resonance area, the top electrode bends upward to form a gap between it and the piezoelectric layer, and a reinforcement structure is formed on the upper surface of the top electrode. The conductivity of the reinforcement structure is greater than the conductivity of the top electrode, and the projection of the reinforcement structure on the substrate is greater than or equal to the projection of the gap on the substrate.

[0006] As an implementable manner, a passivation layer is further provided on the top electrode, the reinforcement structure and the passivation layer are provided on the same layer, the top electrode spans the gap to form a pad, and the passivation layer extends onto the pad.

[0007] As an implementable method, a passivation layer is also provided on the top electrode, the reinforcement structure is provided on the same layer as the passivation layer, the top electrode spans the gap to form a pad, and the reinforcement structure includes a reinforcement portion provided on the gap and a connecting portion provided on the pad.

[0008] As an practicable manner, a passivation layer is further provided on the top electrode, and the reinforcement structure overlaps the edge of the passivation layer.

[0009] As an implementable manner, the top electrode includes an electrode portion disposed in the effective resonance region and a bridging portion disposed on the gap. The reinforcement structure and the bridging portion are made of the same material and are different from the electrode portion.

[0010] As an practicable manner, the material of the top electrode is one of molybdenum, aluminum or tungsten, and the material of the reinforcement structure is one of silver, copper, gold, sodium, zinc, nickel, iron, platinum, tin or lead.

[0011] On the other hand, an embodiment of the present application provides a method for preparing a bulk acoustic wave resonator, including: providing a substrate, and forming a bottom electrode and a piezoelectric layer on the substrate in sequence, wherein an acoustic reflection structure is formed in 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, 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 resonance area, and the sacrificial block is located at the edge of the effective resonance area; forming a reinforcement structure on the upper surface of the top electrode, the conductivity of the reinforcement structure is greater than the conductivity of the top electrode, and the projection of the reinforcement structure on the substrate is greater than the projection of the sacrificial block on the substrate; releasing the sacrificial block to form a gap.

[0012] As an practicable manner, 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, wherein the window overlaps with a projection of the sacrificial block on the substrate; and forming a reinforcement structure in the window.

[0013] As an practicable manner, the reinforcement structure extends to a side of the gap away from the effective resonance region.

[0014] As an implementable method, before forming the reinforcement structure on the top electrode, the preparation method of the bulk acoustic wave resonator also includes: etching the corresponding parts of the top electrode and the sacrificial block to expose the upper surface of the sacrificial block; when forming the reinforcement structure on the top electrode, the part of the reinforcement structure laid on the upper surface of the sacrificial block serves as a bridging part.

[0015] The beneficial effects of the embodiments of the present application include:

[0016] The BAW resonator provided by the present 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 region where the projections of the bottom electrode, piezoelectric layer, top electrode, and acoustic reflection structure overlap on the substrate constitutes an effective resonance region. At the edge of the effective resonance region, the top electrode bends upward to form a gap between the top electrode and the piezoelectric layer. A reinforcement structure is formed on the top surface of the top electrode. The reinforcement structure has a certain thickness. The reinforcement structure and the top electrode simultaneously serve as conductive structures located above the gap, thereby increasing the thickness of the conductive structure located above the gap. The conductivity of the reinforcement structure is greater than that of the top electrode, thereby reducing the resistance of the conductive structure, and thus reducing the resistance of the resonator, thereby improving the Q value of the BAW resonator. The projection of the reinforcement structure on the substrate is greater than or equal to the projection of the gap on the substrate. In addition, the increased thickness of the conductive structure above the gap reduces the risk of fracture of the conductive structure above the gap, thereby improving reliability. Therefore, the BAW resonator of the embodiment of the present application can improve the Q value and reliability of the BAW resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0018] Figure 1 This is one of the structural schematic diagrams of a bulk acoustic wave resonator provided in an embodiment of the present application;

[0019] Figure 2 A second structural diagram of a bulk acoustic wave resonator provided in an embodiment of the present application;

[0020] Figure 3 The third structural diagram of a bulk acoustic wave resonator provided in an embodiment of the present application;

[0021] Figure 4 A fourth structural diagram of a bulk acoustic wave resonator provided in an embodiment of the present application;

[0022] Figure 5 A flow chart of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0023] Figure 6 This is one of the state diagrams of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0024] Figure 7 This is a second state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0025] Figure 8 A third state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0026] Figure 9 A fourth state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0027] Figure 10 A fifth state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0028] Figure 11 A sixth state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0029] Figure 12 The seventh state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0030] Figure 13 This is a state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0031] Figure 14 A ninth state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application;

[0032] Figure 15 This is the tenth state diagram of a method for preparing a bulk acoustic wave resonator provided in an embodiment of the present application.

[0033] Icon: 100-bulk acoustic wave resonator; 110-substrate; 111-acoustic reflection structure; 120-bottom electrode; 130-piezoelectric layer; 140-top electrode; 141-electrode part; 142-bridging part; 150-effective resonance region; 160-gap; 170-reinforcement structure; 171-reinforcement part; 172-connecting part; 180-passivation layer; 190-pad; 210-sacrificial block. DETAILED DESCRIPTION

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present application more clear, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Generally, the components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations.

[0035] Therefore, the following detailed description of the embodiments of the present application provided in the accompanying drawings is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. All other embodiments obtained by persons of ordinary skill in the art based on the embodiments in the present application without creative work are within the scope of protection of the present application.

[0036] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0037] In order to avoid the leakage of lateral sound waves inside the bulk acoustic wave resonator, the existing technology adopts an air gap structure at the edge of the effective resonance area to reflect the sound waves propagating to the edge of the effective resonance area, thereby reducing leakage. In actual applications, the setting of the air gap makes the top electrode bend upward, and the top electrode is mostly formed by vapor deposition. In this way, the thickness of the top electrode is thinner at the inclined surface when bending upward, which increases the resistance of the top electrode, and the thinner position is prone to breakage.

[0038] The embodiment of the present application provides a bulk acoustic wave resonator 100, such as Figures 1 to 4 As shown, it includes a substrate 110 and a bottom electrode 120, a piezoelectric layer 130 and a top electrode 140 sequentially arranged on the substrate 110, an acoustic reflection structure 111 is formed in the substrate 110, and the area where the projections of the bottom electrode 120, the piezoelectric layer 130, the top electrode 140 and the acoustic reflection structure 111 overlap on the substrate 110 is an effective resonance area 150. At the edge of the effective resonance area 150, the top electrode 140 bends upward to form a gap 160 between it and the piezoelectric layer 130, and a reinforcement structure 170 is formed on the upper surface of the top electrode 140. The conductivity of the reinforcement structure 170 is greater than that of the top electrode 140, and the projection of the reinforcement structure 170 on the substrate 110 is greater than or equal to the projection of the gap 160 on the substrate 110.

[0039] The BAW resonator 100 of the embodiment of the present application is used to generate resonance. Specifically, the BAW resonator 100 includes a substrate 110 and a bottom electrode 120, a piezoelectric layer 130, and a top electrode 140 sequentially arranged on the substrate 110. The bottom electrode 120, the piezoelectric layer 130, and the top electrode 140 form a sandwich structure. When the BAW resonator 100 is in operation, 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, thereby forming an electric field 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, a longitudinally propagating acoustic wave is generated in the piezoelectric layer 130.

[0040] In actual applications, there will also be sound waves in the piezoelectric layer 130 that propagate along the plane where the piezoelectric layer 130 is located. At the edge of the effective resonance area 150, the top electrode 140 bends upward to form a gap 160 between the piezoelectric layer 130. The gap 160 is filled with air. The air and the piezoelectric layer 130 have different acoustic reflection coefficients, so that a reflective interface is 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 resonance area 150, the reflective interface reflects the transverse sound wave, thereby avoiding the leakage of the transverse sound wave.

[0041] In the embodiment of the present application, a reinforcement structure 170 is further formed on the upper surface of the top electrode 140. The projection of the reinforcement structure 170 on the substrate 110 is greater than or equal to the projection of the gap 160 on the substrate 110. The reinforcement structure 170 has a certain thickness. The reinforcement structure 170 and the top electrode 140 both serve as conductive structures and are located above the gap 160. This increases the thickness of the conductive structure located above the gap 160. The conductivity of the reinforcement structure 170 is greater than that of the top electrode 140, thereby reducing the resistance of the conductive structure and, in turn, the resistance of the resonator, thereby improving the Q value of the BAW resonator 100. Furthermore, the increased thickness of the conductive structure above the gap 160 reduces the risk of fracture of the conductive structure above the gap 160, thereby improving reliability. Therefore, the BAW resonator 100 of the embodiment of the present application can improve both the Q value and reliability of the BAW resonator 100.

[0042] The specific structure of the sound reflection structure 111 is not limited in the embodiment of the present application, and those skilled in the art can set it according to actual conditions. For example, it can be as follows Figure 1 As shown in the cavity, 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 concave to form a cavity; it can also be a stacked structure formed by alternating high acoustic impedance and low acoustic impedance; it can also be a back-engraved cavity formed by etching the lower surface of the substrate 110.

[0043] In practical applications, a buffer layer or a seed layer may be disposed between the substrate 110 and the bottom electrode 120 to improve the film quality of the piezoelectric layer 130 , thereby improving the performance of the BAW resonator 100 .

[0044] The bulk acoustic wave resonator 100 provided in the present application includes a substrate 110 and a bottom electrode 120, a piezoelectric layer 130 and a top electrode 140 sequentially arranged on the substrate 110. An acoustic reflection structure 111 is formed in the substrate 110. The area where the bottom electrode 120, the piezoelectric layer 130, the top electrode 140 and the acoustic reflection structure 111 overlap on the substrate 110 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 it and the piezoelectric layer 130. A gap 160 is formed on the upper surface of the top electrode 140. A reinforcement structure 170 is formed, and the reinforcement structure 170 has a certain thickness. The reinforcement structure 170 and the top electrode 140 serve as conductive structures and are located above the gap 160. This increases the thickness of the conductive structure located above the gap 160. The conductivity of the reinforcement 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 BAW resonator 100. The projection of the reinforcement 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 above the gap 160 reduces the risk of fracture of the conductive structure above the gap 160, thereby improving reliability. Therefore, the BAW resonator 100 of the present embodiment can improve the Q value and reliability of the BAW resonator 100.

[0045] Optional, such as Figure 1 As shown, a passivation layer 180 is further disposed on the top electrode 140 , the reinforcement structure 170 and the passivation layer 180 are disposed on the same layer, the top electrode 140 spans the gap 160 to form a pad 190 , and the passivation layer 180 extends onto the pad 190 .

[0046] A passivation layer 180 is disposed on the top electrode 140. The passivation layer 180 can isolate the top electrode 140 from the external environment and provide a certain degree of protection for the top electrode 140. The reinforcement structure 170 is disposed on the same layer as the passivation layer 180, and the passivation layer 180 extends onto the pad 190, so that the reinforcement structure 170 is located only on the gap 160. This can minimize the area of ​​the reinforcement structure 170 while ensuring the reinforcement effect.

[0047] In one possible implementation of the embodiment of the present application, Figure 2 As shown, a passivation layer 180 is also provided on the top electrode 140, and the reinforcement structure 170 is provided on the same layer as the passivation layer 180. The top electrode 140 spans the gap 160 to form a pad 190. The reinforcement structure 170 includes a reinforcement portion 171 provided on the gap 160 and a connection portion 172 provided on the pad 190.

[0048] The reinforcement structure 170 is arranged in the same layer as the passivation layer 180, and the top electrode 140 spans the gap 160 to form a pad 190. The reinforcement structure 170 also spans the gap 160 to form a connecting portion 172 located on the pad 190, so that the reinforcement structure 170 includes a reinforcement portion 171 located on the gap 160 and a connecting portion 172 on the pad 190. In this way, the contact area between the reinforcement 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.

[0049] Optional, such as Figure 3 As shown, a passivation layer 180 is further disposed on the top electrode 140 , and the reinforcement structure 170 overlaps the edge of the passivation layer 180 .

[0050] The reinforcement structure 170 is mounted on the edge of the passivation layer 180 , which can increase the contact area of ​​the reinforcement structure 170 , thereby improving the stability of the reinforcement structure 170 .

[0051] In addition, since the reinforcement structure 170 is overlapped on the passivation layer 180, the passivation layer 180 and the reinforcement structure 170 form an interface in the horizontal direction. The passivation layer 180 and the reinforcement structure 170 have different acoustic reflection coefficients, forming a reflective interface at the interface. In this way, the lateral sound waves can be further reflected, thereby further improving the Q value of the bulk acoustic wave resonator 100.

[0052] In one possible implementation of the embodiment of the present application, Figure 4 As shown, the top electrode 140 includes an electrode portion 141 disposed in the effective resonance region 150 and a bridge portion 142 disposed on the gap 160 . The reinforcement structure 170 and the bridge portion 142 are made of the same material and are different from the electrode portion 141 .

[0053] The top electrode 140 located in the effective resonance region 150 and the portion located on the gap 160 are divided into two parts, and the two parts have different conductivities. Specifically, the top electrode 140 located in the effective resonance region 150 is the electrode portion 141, and the bridge portion 142 located on the gap 160. The reinforcement structure 170 is made of the same material as the bridge portion 142, so that the conductivity of the bridge portion 142 is greater than the conductivity 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 wave resonator 100.

[0054] 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. In this way, the reinforcing structure 170 and the bridging portion 142 have better integrity.

[0055] It should be noted that, in the embodiment of the present application, “located on the gap 160 ” refers to a portion located in the same vertical direction as the gap 160 , that is, overlapping with the projection of the gap 160 on the substrate 110 , and does not specifically refer to being directly disposed on the gap 160 .

[0056] Optionally, the material of the top electrode 140 is one of molybdenum, aluminum or tungsten, and the material of the reinforcement structure 170 is one of silver, copper, gold, sodium, zinc, nickel, iron, platinum, tin or lead.

[0057] The material of the top electrode 140 is usually one of molybdenum, aluminum or tungsten, which has a low cost. The material of the reinforcement structure 170 is one of silver, copper, gold, sodium, zinc, nickel, iron, platinum, tin or lead, which has a large electrical conductivity.

[0058] In practical applications, those skilled in the art may also select appropriate materials for the top electrode 140 and the reinforcement structure 170 according to actual conditions, as long as the electrical conductivity of the material of the reinforcement structure 170 is greater than that of the material of the top electrode 140 .

[0059] Another aspect of the present application provides a method for preparing a bulk acoustic wave resonator 100, such as Figure 5 As shown, including:

[0060] S10: Figure 6 and Figure 7 As shown, a substrate 110 is provided, and a bottom electrode 120 and a piezoelectric layer 130 are sequentially formed on the substrate 110, wherein an acoustic reflection structure 111 is formed in the substrate 110;

[0061] Specifically, the method of forming the bottom electrode 120 and the piezoelectric layer 130 is not limited in the embodiment of the present application. For example, chemical vapor deposition, physical vapor deposition, etc. can be used.

[0062] The specific materials of the bottom electrode 120 and the piezoelectric layer 130 are not specifically limited in the embodiments of the present application. Those skilled in the art can choose according to actual conditions, as long as the bottom electrode 120 is conductive and the piezoelectric layer 130 has a piezoelectric effect.

[0063] S20: Figure 7 As shown, a sacrificial block 210 is formed on the piezoelectric layer 130;

[0064] Specifically, the sacrificial block 210 can be formed by depositing a whole layer of sacrificial material on the piezoelectric layer 130 , and then etching using a mask to reserve the sacrificial block 210 at the edge of the effective resonance region 150 .

[0065] Alternatively, a finished sacrificial block 210 may be placed at a preset position.

[0066] S30: Figure 8As shown, a top electrode 140 is formed on the piezoelectric layer 130, and 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 overlap on the substrate 110 is the effective resonance area 150, and the sacrificial block 210 is located at the edge of the effective resonance area 150;

[0067] 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 resonance region 150 , that is, the top electrode 140 bends upward at the edge of the effective resonance region 150 .

[0068] S40: Figure 9 As shown, a reinforcement structure 170 is formed on the upper surface of the top electrode 140 , the conductivity of the reinforcement structure 170 is greater than the conductivity of the top electrode 140 , and the projection of the reinforcement structure 170 on the substrate 110 is greater than the projection of the sacrificial block 210 on the substrate 110 ;

[0069] When forming the reinforcement structure 170 , the entire conductive material may be deposited first and then etched, or a lift-off process may be used.

[0070] S50: Figure 10 and Figure 11 As shown, the sacrificial block 210 is released to form the gap 160 .

[0071] Before releasing the sacrificial layer, the top electrode 140 needs to be patterned to lead out the bottom electrode 120, such as Figure 10 shown.

[0072] In the method for fabricating a BAW resonator 100 according to an embodiment of the present application, a reinforcement structure 170 is formed above the gap 160. The reinforcement structure 170 and the portion of the top electrode 140 located above the gap 160 form a conductive structure. This increases the thickness of the conductive structure located above the gap 160, and the conductivity of the reinforcement structure 170 is greater than that of the top electrode 140. This reduces the resistance of the conductive structure, and thus the resistance of the resonator, thereby improving the Q value of the BAW resonator 100. Furthermore, the increased thickness of the conductive structure above the gap 160 reduces the risk of fracture of the conductive structure above the gap 160, thereby improving reliability. Therefore, the BAW resonator 100 according to an embodiment of the present application can improve both the Q value and reliability of the BAW resonator 100.

[0073] In one possible implementation of the embodiment of the present application, forming the reinforcement structure 170 on the top electrode 140 includes:

[0074] S41: If Figure 8 As shown, a passivation layer 180 is formed on the top electrode 140;

[0075] The passivation layer 180 is used to isolate the top electrode 140 from the external environment and plays a certain protective role for the top electrode 140 .

[0076] S42: Figure 8 As shown, the passivation layer 180 is etched to form a window, which overlaps with the projection of the sacrificial block 210 on the substrate 110;

[0077] In the embodiment of the present application, the passivation layer 180 is etched to form a window, and the passivation layer 180 can also be used as a template to prepare the reinforcement structure 170.

[0078] S43: If Figure 9 As shown, a reinforcement structure 170 is formed within the window.

[0079] The specific structure of the reinforcement structure 170 has been described in detail in the introduction of the BAW resonator 100 and will not be repeated here.

[0080] Optional, such as Figure 12 As shown, the reinforcement structure 170 extends to a side of the gap 160 away from the effective resonance region 150 .

[0081] Specifically, the reinforcement structure 170 includes a reinforcement portion 171 disposed on the gap 160 and a connection portion 172 disposed on the pad 190. This increases the contact area between the reinforcement structure 170 and the top electrode 140, further reducing the resistance of the top electrode 140 and thereby improving the Q value of the BAW resonator 100.

[0082] The reinforcement structure 170 may also extend to the upper surface of the passivation layer 180, such as Figure 13 As shown, the contact area of ​​the reinforcement structure 170 can be increased, thereby improving the stability of the reinforcement structure 170.

[0083] In one possible implementation of the embodiment of the present application, before forming the reinforcement structure 170 on the top electrode 140 , the method for preparing the BAW resonator 100 further includes:

[0084] S61: If Figure 14 As shown, the portion corresponding to the top electrode 140 and the sacrificial block 210 is etched to expose the upper surface of the sacrificial block 210;

[0085] S62: If Figure 15 As described above, when the reinforcement structure 170 is formed on the top electrode 140 , the portion of the reinforcement structure 170 laid on the upper surface of the sacrificial block 210 serves as the bridging portion 142 .

[0086] In this way, the top electrode 140 includes an electrode portion 141 arranged in the effective resonance region 150 and a bridge portion 142 arranged on the gap 160, wherein the reinforcement structure 170 is made of the same material as the bridge portion 142, so that the conductivity of the bridge portion 142 is greater than the conductivity 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 wave resonator 100.

[0087] The reinforcing structure 170 and the bridging portion 142 are made of the same material and can be formed in the same deposition step. In this way, the reinforcing structure 170 and the bridging portion 142 have better integrity.

[0088] The foregoing description is merely a preferred embodiment of the present application and is not intended to limit the present application. Persons skilled in the art will readily appreciate that various modifications and variations are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present application shall be included within the scope of protection of the present application.

Claims

1. A bulk acoustic wave resonator, characterized in that: The invention comprises a substrate and a bottom electrode, a piezoelectric layer and a top electrode sequentially arranged on the substrate, wherein an acoustic reflection structure is formed in the substrate, and an area where the projections of the bottom electrode, the piezoelectric layer, the top electrode and the acoustic reflection structure overlap on the substrate is an effective resonance area, and at the edge of the effective resonance area, the top electrode bends upward to form a gap with the piezoelectric layer, and a reinforcement structure is formed on the upper surface of the top electrode, the conductivity of the reinforcement structure is greater than the conductivity of the top electrode, and the projection of the reinforcement structure on the substrate is greater than or equal to the projection of the gap on the substrate; a passivation layer is also provided on the top electrode, the reinforcement structure is provided on the same layer as the passivation layer, the top electrode spans the gap to form a pad, the reinforcement structure comprises a reinforcement portion provided on the gap and a connecting portion provided on the pad; the top electrode comprises an electrode portion provided in the effective resonance area and a bridging portion provided on the gap, the reinforcement structure and the bridging portion are made of the same material and are both different from the electrode portion.

2. The bulk acoustic wave resonator according to claim 1, wherein The reinforcement structure overlaps the edge of the passivation layer.

3. The bulk acoustic wave resonator according to any one of claims 1 to 2, characterized in that: The material of the top electrode is one of molybdenum, aluminum or tungsten, and the material of the reinforcement structure is one of silver, copper, gold, sodium, zinc, nickel, iron, platinum, tin or lead.

4. A method for preparing a bulk acoustic wave resonator, characterized in that: For preparing the bulk acoustic wave resonator according to any one of claims 1 to 3, comprising: Providing a substrate, and sequentially forming a bottom electrode and a piezoelectric layer on the substrate, wherein an acoustic reflection structure is formed in 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, an effective resonance region formed by overlapping projections of the bottom electrode, the piezoelectric layer, the top electrode, and the acoustic reflection structure on the substrate, and the sacrificial block being located at an edge of the effective resonance region; forming a reinforcement structure on the upper surface of the top electrode, wherein the conductivity of the reinforcement structure is greater than the conductivity of the top electrode, and the projection of the reinforcement structure on the substrate is greater than the projection of the sacrificial block on the substrate; The sacrificial block is released to form a gap.

5. The method for preparing a bulk acoustic wave resonator according to claim 4, characterized in that: The step of forming a reinforcement structure on the top electrode comprises: forming a passivation layer on the top electrode; etching the passivation layer to form a window, wherein the window overlaps with a projection of the sacrificial block on the substrate; A reinforcement structure is formed within the window.

6. The method for preparing a bulk acoustic wave resonator according to claim 5, wherein: The reinforcement structure extends to a side of the gap away from the effective resonance region.

7. The method for preparing a bulk acoustic wave resonator according to claim 4, wherein: Before forming a reinforcement structure on the top electrode, the method further includes: Etching the top electrode and the corresponding portion of the sacrificial block to expose the upper surface of the sacrificial block; When forming a reinforcement structure on the top electrode, a portion of the reinforcement structure laid on the upper surface of the sacrificial block serves as a bridging portion.

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