A high electrical performance bulk acoustic wave resonator, preparation method and bulk acoustic wave filter

Abstract

The present application relates to the technical field of bulk acoustic wave resonators, and specifically provides a bulk acoustic wave resonator with high electrical performance, a preparation method, and a bulk acoustic wave filter. The method comprises the following steps: sequentially forming a buffer layer, a piezoelectric layer, and a patterned top electrode on a first substrate; forming a blind hole outside the patterned top electrode; forming a first interconnection line on the top surface of the patterned top electrode and forming a second interconnection line on the top surface of the piezoelectric layer by filling the blind hole; bonding a second substrate to the first interconnection line and the second interconnection line; inverting an etching assembly and then etching the first substrate; forming a patterned bottom electrode in a groove and then attaching a cover layer to the first substrate; removing the second substrate and then fixing the bulk acoustic wave resonator to a packaging substrate via the first interconnection line and the second interconnection line. The method can effectively solve the problem of bulging or cracking of the bulk acoustic wave resonator film during the process of releasing the sacrificial layer and partial energy leakage of the bulk acoustic wave resonator.

Description

Technical Field

[0001] The present application relates to the technical field of bulk acoustic wave resonators, and in particular to a bulk acoustic wave resonator with high electrical performance, a preparation method thereof, and a bulk acoustic wave filter. Background Art

[0002] BAW resonators (BAWs) are electrical devices that convert electrical and mechanical energy through the piezoelectric effect of piezoelectric materials and, using unique boundary conditions, create resonance in mechanical waves. Because BAWs can produce high-quality resonance peaks, they are widely used in fields such as communication filtering and navigation positioning.

[0003] The specific process of the related BAW resonator preparation method is as follows: forming a groove on a substrate; filling the groove with a sacrificial layer; forming a bottom electrode, a piezoelectric layer, and a top electrode on the substrate in sequence; and removing the sacrificial layer to form a BAW resonator whose acoustic reflector is an air cavity. Since the bottom electrode and the top electrode formed on the substrate both span the air cavity, and the top and bottom electrodes spanning the air cavity will inevitably generate noise, which will leak out of the BAW resonator. Therefore, the related art has the problem that due to the noise generated by the top and bottom electrodes spanning the air cavity, part of the energy of the BAW resonator leaks, thereby causing the electrical performance of the BAW resonator to deteriorate. In addition, since the BAW resonator film (bottom electrode, piezoelectric layer, and top electrode) may be subjected to excessive stress and / or uneven stress distribution during the release of the sacrificial layer, the related art also has the problem that the BAW resonator film may rupture or crack during the release of the sacrificial layer.

[0004] There is no effective technical solution to the above problems. It should be noted that the above information disclosed in this section is only used to understand the background of the present invention, and therefore may contain information that does not constitute prior art. Summary of the Invention

[0005] The purpose of the present application is to provide a high-electrical-performance bulk acoustic wave resonator, a preparation method, and a bulk acoustic wave filter, which can effectively solve the problems of excessive stress or uneven stress distribution on the bulk acoustic wave resonator film during the release of the sacrificial layer, which may cause the bulk acoustic wave resonator film to develop a tympanic membrane or crack during the release of the sacrificial layer, and partial energy leakage of the bulk acoustic wave resonator due to the generation of interference waves between the bottom electrode and the top electrode across the air cavity.

[0006] In a first aspect, the present application provides a method for preparing a bulk acoustic wave resonator with high electrical performance, which comprises the following steps:

[0007] S1. Forming a buffer layer, a piezoelectric layer, and a patterned top electrode in sequence on a first substrate, wherein the patterned top electrode partially covers the piezoelectric layer;

[0008] S2. forming a blind hole outside the patterned top electrode, penetrating the piezoelectric layer and the buffer layer and having a depth greater than 0 on the first substrate;

[0009] S3, forming a first interconnection line on the top surface of the patterned top electrode and forming a second interconnection line on the top surface of the piezoelectric layer by filling a blind hole, wherein the second interconnection line is located outside the patterned top electrode;

[0010] S4, bonding a second substrate to the first interconnection line and the second interconnection line to obtain an etched assembly, with a gap between the second substrate and the patterned top electrode;

[0011] S5, inverting the etching assembly, and then etching the first substrate to form a groove on the first substrate to expose the buffer layer and the second interconnection line;

[0012] S6, forming a patterned bottom electrode in the groove, which is connected to the second interconnection line and has a top surface height smaller than a top surface height of the first substrate, and then mounting a cover film layer on the first substrate to form a bulk acoustic wave resonator;

[0013] S7 , removing the second substrate, then fixing the BAW resonator on the packaging substrate through the first interconnection line and the second interconnection line, and performing plastic packaging on the BAW resonator.

[0014] The present application provides a method for preparing a high-electrical-performance bulk acoustic wave resonator, which can form an acoustic reflector of the bulk acoustic wave resonator by first etching a first substrate, then forming a patterned bottom electrode in the groove, and finally forming a coating layer on the first substrate. That is, the present application does not require forming a sacrificial layer and releasing the sacrificial layer on the substrate. Therefore, the present application can effectively solve the problem of tympanic membrane or cracking of the bulk acoustic wave resonator film during the release of the sacrificial layer due to excessive stress or uneven stress distribution during the release of the sacrificial layer. Moreover, since the bottom electrode of the present application does not span the air cavity, the present application can also effectively solve the problem of partial energy leakage of the bulk acoustic wave resonator due to the generation of interference waves by the bottom electrode and top electrode spanning the air cavity, thereby effectively improving the electrical performance of the bulk acoustic wave resonator.

[0015] Optionally, step S1 includes:

[0016] S11, forming a buffer layer on a first substrate;

[0017] S12, depositing single crystal aluminum nitride on the buffer layer based on a deposition process to form a piezoelectric layer on the buffer layer;

[0018] S13. Forming a patterned top electrode on the piezoelectric layer based on a deposition process and a patterning process.

[0019] This technical solution is equivalent to using single-crystal aluminum nitride as the material for the piezoelectric layer. Since the piezoelectric layer made of single-crystal aluminum nitride has a low dislocation density and an atomically smooth surface, this technical solution can effectively improve the effective electromechanical coupling coefficient of the bulk acoustic wave resonator and improve the insertion loss of the bulk acoustic wave filter passband, thereby effectively improving the electrical performance of the bulk acoustic wave resonator and the bulk acoustic wave filter.

[0020] Optionally, step S1 further includes the following steps performed before step S11:

[0021] S14, cleaning the first substrate.

[0022] This technical solution is equivalent to first cleaning the first substrate and then forming a buffer layer on the first substrate. Since this technical solution can remove organic matter on the surface of the first substrate by cleaning the first substrate, this technical solution can effectively improve the growth quality of the buffer layer, piezoelectric layer and patterned top electrode.

[0023] Optionally, step S5 includes:

[0024] S51, turning the etching assembly upside down;

[0025] S52, thinning the first substrate so that a distance between a top surface of the first substrate and a top surface of the second interconnection line is a preset distance;

[0026] S53 , etching the first substrate based on a dry etching process to form a groove on the first substrate to expose the buffer layer and the second interconnection line.

[0027] Since this technical solution thins the first substrate before etching it, that is, this technical solution can effectively reduce the thickness of the first substrate, and thus this technical solution can effectively reduce the etching depth, thereby effectively improving the etching efficiency of the first substrate, and this technical solution can reduce the size of the ultimately formed bulk acoustic wave resonator by reducing the thickness of the first substrate.

[0028] Optionally, the package substrate has a third interconnection line, and step S7 includes:

[0029] S71, removing the second substrate based on a lift-off process;

[0030] S72, welding the first interconnection line, the second interconnection line, and the third interconnection line based on a flip-chip process to fix the BAW resonator on the packaging substrate;

[0031] S73. Plastic-encapsulate the bulk acoustic wave resonator based on a plastic-encapsulation process.

[0032] In the second aspect, the present application also provides a high electrical performance bulk acoustic wave resonator, which includes a bulk acoustic wave resonator, a packaging substrate and a plastic packaging layer. The bulk acoustic wave resonator includes a first substrate, a buffer layer, a piezoelectric layer, a patterned top electrode, a first interconnection line, a second interconnection line, a patterned bottom electrode, a covering layer and a first air cavity. The two ends of the first interconnection line are respectively connected to the patterned top electrode and the packaging substrate, the second interconnection line is connected to the piezoelectric layer and the packaging substrate, the second interconnection line passes through the piezoelectric layer and the buffer layer and the depth on the first substrate is greater than 0, the patterned bottom electrode is connected to the buffer layer and the second interconnection line, the first substrate is arranged around the patterned bottom electrode, the covering layer is connected to the top surface of the first substrate and there is a gap between it and the patterned bottom electrode, the first air cavity is enclosed by the first substrate, the second interconnection line, the patterned bottom electrode and the covering layer, and the plastic packaging layer is arranged on the packaging substrate and wraps around the outside of the bulk acoustic wave resonator.

[0033] The present application provides a high-electrical-performance bulk acoustic wave resonator, which utilizes a first substrate, a second interconnect, a patterned bottom electrode, and a covering layer to enclose a first air cavity. That is, the present application does not require forming a sacrificial layer or releasing the sacrificial layer on the substrate. Therefore, the present application can effectively solve the problem of excessive stress or uneven stress distribution on the bulk acoustic wave resonator film during the release of the sacrificial layer, which may cause the bulk acoustic wave resonator film to rupture or crack during the release of the sacrificial layer. Moreover, since the bottom electrode of the present application does not span the air cavity, the present application can also effectively solve the problem of partial energy leakage of the bulk acoustic wave resonator due to the generation of interference waves by the bottom electrode and top electrode spanning the air cavity, thereby effectively improving the electrical performance of the bulk acoustic wave resonator.

[0034] Optionally, the patterned bottom electrode and the patterned top electrode are staggered.

[0035] Since the patterned bottom electrode of this technical solution is located in the first air cavity, that is, the patterned bottom electrode is located in the effective area of ​​the bulk acoustic wave resonator, that is, there is only a patterned top electrode outside the effective area of ​​the bulk acoustic wave resonator, so this technical solution can effectively avoid the situation where energy leakage occurs due to the piezoelectric effect generated by the patterned bottom electrode located outside the effective area of ​​the bulk acoustic wave resonator and the top electrode located outside the effective area of ​​the bulk acoustic wave resonator. The existing technology can prevent energy leakage by setting an air gap in the external area of ​​the interconnection line of the top electrode, but setting an air gap will make the processing technology of the bulk acoustic wave resonator complicated. Since there is no patterned bottom electrode in the external area of ​​the interconnection line of the patterned top electrode of this technical solution, this technical solution does not need to set an air gap in the external area of ​​the interconnection line of the patterned top electrode to prevent energy leakage, thereby effectively simplifying the processing technology of the bulk acoustic wave resonator.

[0036] Optionally, the second interconnection line is located at an edge of the patterned bottom electrode.

[0037] Since the second interconnection line of this technical solution passes through the piezoelectric layer and is located at the edge of the patterned bottom electrode, this technical solution can effectively avoid the situation where the piezoelectric layer structure located in the central area of ​​the BAW resonator is destroyed due to the second interconnection line being located in the central area of ​​the BAW resonator, thereby affecting the electrical performance of the BAW resonator.

[0038] Optionally, there are multiple second interconnection lines.

[0039] In a third aspect, the present application further provides a bulk acoustic wave filter, which includes a plurality of high electrical performance bulk acoustic wave resonators provided in the second aspect.

[0040] The present application provides a bulk acoustic wave filter, which utilizes a first substrate, a second interconnect line, a patterned bottom electrode, and a covering layer to enclose a first air cavity. That is, the present application does not require forming a sacrificial layer and releasing the sacrificial layer on the substrate. Therefore, the present application can effectively solve the problem of excessive stress or uneven stress distribution on the thin film of the bulk acoustic wave resonator during the release of the sacrificial layer, which may cause the thin film of the bulk acoustic wave resonator to develop a tympanic membrane or crack during the release of the sacrificial layer. Moreover, since the bottom electrode of the present application does not span the air cavity, the present application can also effectively solve the problem of partial energy leakage of the bulk acoustic wave resonator due to the generation of interference waves by the bottom electrode and top electrode spanning the air cavity, thereby effectively improving the electrical performance of the bulk acoustic wave resonator.

[0041] From the above, it can be seen that the present application provides a high electrical performance bulk acoustic wave resonator, a preparation method and a bulk acoustic wave filter, which can form an acoustic reflector of the bulk acoustic wave resonator by first etching the first substrate, then forming a patterned bottom electrode in the groove, and finally forming a coating layer on the first substrate. That is, the present application does not need to form a sacrificial layer and release the sacrificial layer on the substrate. Therefore, the present application can effectively solve the problem of tympanic membrane or cracking of the bulk acoustic wave resonator film during the release of the sacrificial layer due to excessive stress or uneven stress distribution during the release of the sacrificial layer. Moreover, since the bottom electrode of the present application does not span the air cavity, the present application can also effectively solve the problem of partial energy leakage of the bulk acoustic wave resonator due to the generation of interference waves by the bottom electrode and the top electrode spanning the air cavity, thereby effectively improving the electrical performance of the bulk acoustic wave resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A flow chart of a method for preparing a bulk acoustic wave resonator with high electrical performance provided in an embodiment of the present application.

[0043] Figure 2 A schematic diagram of a method for preparing a bulk acoustic wave resonator with high electrical performance provided in an embodiment of the present application.

[0044] Figure 3 A schematic structural diagram of a high electrical performance bulk acoustic wave resonator provided in an embodiment of the present application.

[0045] Figure 4 This is a schematic top view of the structure of a bulk acoustic wave filter provided in an embodiment of the present application, which does not include a plastic packaging layer and a covering layer.

[0046] Figure 5 This is a schematic cross-sectional structural diagram of a bulk acoustic wave filter provided in the first embodiment of the present application.

[0047] Figure 6 This is a schematic cross-sectional structural diagram of a bulk acoustic wave filter provided in the second embodiment of the present application.

[0048] Figure 7 This is a schematic cross-sectional structural diagram of a bulk acoustic wave filter provided in the third embodiment of the present application.

[0049] Figure numerals: 1. first substrate; 2. buffer layer; 3. piezoelectric layer; 4. patterned top electrode; 5. blind hole; 6. first interconnection line; 7. second interconnection line; 8. second substrate; 9. groove; 10. patterned bottom electrode; 11. coating layer; 12. packaging substrate; 13. plastic encapsulation layer; 14. first air cavity; 15. second air cavity; 16. third interconnection line. DETAILED DESCRIPTION

[0050] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The components of the embodiments of the present application generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those skilled in the art without making creative work fall within the scope of protection of the present application.

[0051] It should be noted that similar reference numerals and letters represent similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings. At the same time, in the description of this application, the terms "first", "second", etc. are only used to distinguish the description and should not be understood as indicating or implying relative importance.

[0052] First, as Figure 1-Figure 2 As shown, the present application provides a method for preparing a bulk acoustic wave resonator with high electrical performance, which includes the following steps:

[0053] S1, forming a buffer layer 2, a piezoelectric layer 3 and a patterned top electrode 4 in sequence on a first substrate 1, wherein the patterned top electrode 4 partially covers the piezoelectric layer 3;

[0054] S2, forming a blind hole 5 outside the patterned top electrode 4, penetrating the piezoelectric layer 3 and the buffer layer 2 and having a depth greater than 0 on the first substrate 1;

[0055] S3, forming a first interconnection line 6 on the top surface of the patterned top electrode 4 and forming a second interconnection line 7 on the top surface of the piezoelectric layer 3 by filling the blind hole 5, the second interconnection line 7 being located outside the patterned top electrode 4;

[0056] S4, bonding a second substrate 8 on the first interconnection line 6 and the second interconnection line 7 to obtain an etched assembly, with a gap between the second substrate 8 and the patterned top electrode 4;

[0057] S5, inverting the etching assembly, and then etching the first substrate 1 to form a groove 9 on the first substrate 1 to expose the buffer layer 2 and the second interconnection line 7;

[0058] S6. Forming a patterned bottom electrode 10 in the groove 9, which is connected to the second interconnection line 7 and has a top surface height smaller than that of the first substrate 1, and then attaching a cover layer 11 on the first substrate 1 to form a bulk acoustic wave resonator;

[0059] S7 , removing the second substrate 8 , and then fixing the BAW resonator on the packaging substrate 12 through the first interconnection line 6 and the second interconnection line 7 and performing plastic packaging on the BAW resonator.

[0060] Among them, the material of the first substrate 1 in step S1 can be sapphire, spinel, silicon carbide or silicon, and step S1 can form a buffer layer 2, a piezoelectric layer 3 and a patterned top electrode 4 on the first substrate 1 in sequence based on an existing thin film formation process. Since this embodiment first forms the buffer layer 2 on the first substrate 1, and then forms the piezoelectric layer 3 and the patterned top electrode 4 on the buffer layer 2 in sequence, and the lattice mismatch rate between the first substrate 1 and the piezoelectric layer 3 is greater than the lattice mismatch rate between the buffer layer 2 and the first substrate 1, this embodiment can effectively avoid the situation where the piezoelectric layer 3 directly grown on the first substrate 1 and the patterned top electrode 4 grown on the piezoelectric layer 3 have lattice defects due to the excessive lattice mismatch rate between the first substrate 1 and the piezoelectric layer 3. The material of the buffer layer 2 in this embodiment is preferably aluminum nitride, and the thickness of the buffer layer 2 in this embodiment is preferably 10-50nm. The material of the top electrode of this embodiment is a metal material with high electrical conductivity, large acoustic impedance and large Young's modulus. The material of the top electrode is preferably any one or more of aluminum, copper, gold, molybdenum, titanium, tungsten, ruthenium and platinum.

[0061] In step S2 , a blind hole 5 with a depth greater than 0 and penetrating the piezoelectric layer 3 and the buffer layer 2 is formed outside the patterned top electrode 4 by etching the area outside the patterned top electrode 4 based on an etching process.

[0062] Step S3 can form a first interconnect 6 on the top surface of the patterned top electrode 4 and a second interconnect 7 on the top surface of the piezoelectric layer 3 based on existing thin film growth and photolithography processes. That is, the first interconnect 6 in this embodiment is connected only to the patterned top electrode 4, and the second interconnect 7 in this embodiment is connected to the first substrate 1, the piezoelectric layer 3, and the buffer layer 2. Since step S6 forms a patterned bottom electrode 10 connected to the second interconnect 7, to avoid affecting the resonant frequency and quality factor of the bulk acoustic wave resonator due to the interconnection between the patterned top electrode 4 and the patterned bottom electrode 10, the second interconnect 7 formed in step S3 is located outside the patterned top electrode 4, that is, the second interconnect 7 is not connected to the patterned top electrode 4. Preferably, the height of the top surface of the first interconnect 6 in this embodiment is the same as the height of the top surface of the second interconnect 7. The material of the first interconnect 6 and the second interconnect 7 in this embodiment is preferably any one or more conductive metal materials such as titanium, copper, aluminum, gold, and tungsten. The material of the first interconnect 6 in this embodiment is preferably the same as the material of the second interconnect 7.

[0063] In step S4, a second substrate 8 can be bonded to the first interconnect 6 and the second interconnect 7 using an existing bonding process. The second substrate 8 is preferably a silicon substrate. In steps S5 and S6, the second substrate 8 can protect the patterned top electrode 4 and the piezoelectric layer 3 and support the structures located thereon. Since the depth of the second interconnect 7 on the first substrate 1 is greater than zero, meaning that a portion of the second interconnect 7 is located within the first substrate 1, step S5 can be performed by etching the first substrate 1 to form a recess 9 in the first substrate 1 that exposes the buffer layer 2 and the second interconnect 7. It should be understood that step S6 forms a patterned bottom electrode 10 connected to the second interconnect 7 within the recess 9. The contact area between the patterned bottom electrode 10 and the second interconnect 7 is correlated with the exposed area of ​​the second interconnect 7. The electrical connection between the patterned bottom electrode 10 and the second interconnect 7 is positively correlated with the contact area between the patterned bottom electrode 10 and the second interconnect 7. Therefore, after etching the first substrate 1, in this embodiment, the side surfaces and a portion of the top surface of the second interconnect 7 are preferably exposed.

[0064] The process of forming the patterned bottom electrode 10 in the groove 9 in step S6 is preferably the same as the process of forming the patterned top electrode 4 on the piezoelectric layer 3 in step S1. The material of the patterned bottom electrode 10 in this embodiment is preferably the same as the material of the patterned top electrode 4. The patterned bottom electrode 10 in step S6 is connected to the second interconnection line 7 by contacting the side of the second interconnection line 7. After the patterned bottom electrode 10 is formed, step S6 can be based on the existing coating process to mount a coating layer 11 on the first substrate 1. The coating layer 11 is preferably a blue film or a UV film. The material of the coating layer 11 is preferably polyvinyl chloride (PVC), polypropylene (BO Any one or more of PP) and polyester (PET), since the top surface height of the patterned bottom electrode 10 is smaller than the top surface height of the first substrate 1, and the film layer 11 of this embodiment is attached to the first substrate 1, after the film layer 11 is formed, the film layer 11 of this embodiment, the first substrate 1, the second interconnection line 7 and the patterned bottom electrode 10 enclose a first air cavity 14. The first air cavity 14 and the patterned bottom electrode 10, the buffer layer 2, the piezoelectric layer 3, the first interconnection line 6, the second interconnection line 7 and the patterned top electrode 4 form a bulk acoustic wave resonator, that is, the first air cavity 14 of this embodiment is an acoustic reflection mirror of the bulk acoustic wave resonator. It should be understood that, since the first air cavity 14 of this embodiment is formed by enclosing the coating layer 11, the first substrate 1, the second interconnection line 7 and the patterned bottom electrode 10, and the second interconnection line 7 of this embodiment is located outside the patterned top electrode 4, this embodiment is equivalent to making the bottom electrode not span the air cavity. Since when the patterned bottom electrode 10 partially spans the air cavity, even if the patterned top electrode 4 spans the air cavity, the patterned top electrode 4 spanning the cavity will not generate noise with the patterned bottom electrode 10. Therefore, this embodiment can effectively avoid the situation where noise is generated due to both the bottom electrode and the top electrode spanning the air cavity.

[0065] After removing the second substrate 8, step S7 can fix the BAW resonator on the packaging substrate 12 by welding the first interconnection line 6 and the second interconnection line 7 to the packaging substrate 12, and then plastic-encapsulate the BAW resonator based on the existing plastic encapsulation process. The packaging substrate 12 of this embodiment is preferably a ceramic substrate and a resin substrate. After the BAW resonator is fixed on the packaging substrate 12, the packaging substrate 12 and the BAW resonator will enclose a second air cavity 15, which can protect the piezoelectric layer 3 and the patterned top electrode 4. After the plastic encapsulation is completed, the plastic encapsulation layer 13 can protect the BAW resonator. The material of the plastic encapsulation layer 13 of this embodiment is preferably epoxy resin.

[0066] The present application provides a method for preparing a high-electrical-performance bulk acoustic wave resonator, which can form an acoustic reflector of the bulk acoustic wave resonator by first etching the first substrate 1, then forming a patterned bottom electrode 10 in the groove 9, and finally forming a coating layer 11 on the first substrate 1. That is, the present application does not need to form a sacrificial layer and release the sacrificial layer on the substrate. Therefore, the present application can effectively solve the problem of tympanic membrane or cracking of the bulk acoustic wave resonator film during the release of the sacrificial layer due to excessive stress or uneven stress distribution during the release of the sacrificial layer. Moreover, since the bottom electrode of the present application does not span the air cavity, the present application can also effectively solve the problem of partial energy leakage of the bulk acoustic wave resonator due to the generation of interference waves by the bottom electrode and top electrode spanning the air cavity, thereby effectively improving the electrical performance of the bulk acoustic wave resonator.

[0067] In some preferred embodiments, step S1 includes:

[0068] S11, forming a buffer layer 2 on a first substrate 1;

[0069] S12, depositing single-crystal aluminum nitride on the buffer layer 2 based on a deposition process to form a piezoelectric layer 3 on the buffer layer 2;

[0070] S13 , forming a patterned top electrode 4 on the piezoelectric layer 3 based on a deposition process and a patterning process.

[0071] Step S12 preferably deposits single-crystal aluminum nitride on the buffer layer 2 based on a metal organic chemical vapor deposition process, that is, this embodiment is equivalent to using single-crystal aluminum nitride as the material of the piezoelectric layer 3. Since the piezoelectric layer 3 made of single-crystal aluminum nitride has a low dislocation density and an atomically smooth surface, this embodiment can effectively improve the effective electromechanical coupling coefficient of the bulk acoustic wave resonator and improve the insertion loss of the bulk acoustic wave filter passband, thereby effectively improving the electrical performance of the bulk acoustic wave resonator and the bulk acoustic wave filter. It should be understood that it is difficult for the existing technology to deposit single-crystal aluminum nitride on a sacrificial layer, that is, it is difficult for the existing technology to improve the electrical performance of the bulk acoustic wave resonator by forming a piezoelectric layer 3 whose material is single-crystal aluminum nitride on a substrate. Since this embodiment does not require the formation of a sacrificial layer on the substrate, and this embodiment can form a piezoelectric layer 3 whose material is single-crystal aluminum nitride on the first substrate 1 by first forming a buffer layer 2 on the first substrate 1 and then depositing single-crystal aluminum nitride on the buffer layer 2, this embodiment can improve the electrical performance of the bulk acoustic wave resonator by forming a piezoelectric layer 3 whose material is single-crystal aluminum nitride on the substrate.

[0072] In some preferred embodiments, step S1 further includes the following steps performed before step S11:

[0073] S14, cleaning the first substrate 1.

[0074] This embodiment is equivalent to first cleaning the first substrate 1 and then forming a buffer layer 2 on the first substrate 1. Since this embodiment can remove organic matter on the surface of the first substrate 1 by cleaning the first substrate 1, this embodiment can effectively improve the growth quality of the buffer layer 2, the piezoelectric layer 3 and the patterned top electrode 4.

[0075] In some preferred embodiments, step S5 includes:

[0076] S51, turning the etching assembly upside down;

[0077] S52, thinning the first substrate 1 so that the distance between the top surface of the first substrate 1 and the top surface of the second interconnection line 7 is a preset distance;

[0078] S53 , etching the first substrate 1 based on a dry etching process to form a groove 9 on the first substrate 1 to expose the buffer layer 2 and the second interconnection line 7 .

[0079] Since this embodiment thins the first substrate 1 before etching the first substrate 1, that is, this embodiment can effectively reduce the thickness of the first substrate 1, and thus this embodiment can effectively reduce the etching depth, thereby effectively improving the etching efficiency of the first substrate 1, and this embodiment can reduce the size of the ultimately formed bulk acoustic wave resonator by reducing the thickness of the first substrate 1.

[0080] In some preferred embodiments, the package substrate 12 has a third interconnection line 16, and step S7 includes:

[0081] S71, removing the second substrate 8 based on a lift-off process;

[0082] S72, welding the first interconnection line 6, the second interconnection line 7 and the third interconnection line 16 based on a flip-chip process to fix the BAW resonator on the packaging substrate 12;

[0083] S73. Plastic-encapsulate the bulk acoustic wave resonator based on a plastic-encapsulation process.

[0084] Since the packaging substrate 12 of this embodiment has a third interconnection line 16, and step S72 welds the first interconnection line 6 and the second interconnection line 7 to the third interconnection line 16 based on the flip-chip process, this embodiment can apply a voltage signal or an electric signal to the patterned top electrode 4 through the third interconnection line 16 and the first interconnection line 6. This embodiment can apply a voltage signal or an electric signal to the patterned bottom electrode 10 through the third interconnection line 16 and the second interconnection line 7. When a voltage signal or an electric signal is applied to the patterned top electrode 4 and the patterned bottom electrode 10, an electric field is formed at both ends of the piezoelectric layer 3 to excite bulk acoustic waves (equivalent to exciting the piezoelectric layer 3 to generate longitudinal waves), thereby realizing the mutual conversion of electrical energy and mechanical energy and the frequency selection of the bulk acoustic wave resonator.

[0085] From the above, it can be seen that the present application provides a method for preparing a high-electrical-performance bulk acoustic wave resonator, which can form an acoustic reflector of the bulk acoustic wave resonator by first etching the first substrate 1, then forming a patterned bottom electrode 10 in the groove 9, and finally forming a coating layer 11 on the first substrate 1. That is, the present application does not need to form a sacrificial layer and release the sacrificial layer on the substrate. Therefore, the present application can effectively solve the problem of tympanic membrane or cracking of the bulk acoustic wave resonator film during the release of the sacrificial layer due to excessive stress or uneven stress distribution in the process of releasing the sacrificial layer. Moreover, since the bottom electrode of the present application does not span the air cavity, the present application can also effectively solve the problem of partial energy leakage of the bulk acoustic wave resonator due to the generation of interference waves by the bottom electrode and the top electrode spanning the air cavity, thereby effectively improving the electrical performance of the bulk acoustic wave resonator.

[0086] Second, as Figure 3 As shown, the present application also provides a high electrical performance bulk acoustic wave resonator, which includes a bulk acoustic wave resonator, a packaging substrate 12 and a plastic packaging layer 13. The bulk acoustic wave resonator includes a first substrate 1, a buffer layer 2, a piezoelectric layer 3, a patterned top electrode 4, a first interconnection line 6, a second interconnection line 7, a patterned bottom electrode 10, a coating layer 11 and a first air cavity 14. The two ends of the first interconnection line 6 are respectively connected to the patterned top electrode 4 and the packaging substrate 12, and the second interconnection line 7 is connected to the piezoelectric layer 3 and the packaging substrate 12. The second interconnection line 7 passes through the piezoelectric layer 3 and the buffer layer 2 and has a depth greater than 0 on the first substrate 1. The patterned bottom electrode 10 is connected to the buffer layer 2 and the second interconnection line 7. The first substrate 1 is arranged around the patterned bottom electrode 10. The coating layer 11 is connected to the top surface of the first substrate 1 and there is a gap between it and the patterned bottom electrode 10. The first air cavity 14 is formed by the first substrate 1, the second interconnection line 7, the patterned bottom electrode 10 and the coating layer 11. The plastic encapsulation layer 13 is arranged on the packaging substrate 12 and wraps around the outside of the bulk acoustic wave resonator.

[0087] An embodiment of the present application provides a high-electrical-performance BAW resonator. The high-electrical-performance BAW resonator provided in this embodiment is preferably manufactured by the high-electrical-performance BAW resonator manufacturing method provided in the first aspect described above. The principle of the high-electrical-performance BAW resonator provided in this embodiment is the same as the principle of the high-electrical-performance BAW resonator manufacturing method provided in the first aspect described above, and will not be discussed in detail here. It should be understood that because the first substrate 1 of this embodiment is disposed around the patterned bottom electrode 10, the outer boundary of the projection of the patterned bottom electrode 10 in this embodiment in the top-view direction is located within the inner boundary of the projection of the first substrate 1 in the top-view direction.

[0088] In some preferred embodiments, the patterned bottom electrode 10 is staggered with the patterned top electrode 4. Since the patterned bottom electrode 10 of this embodiment is located within the first air cavity 14, that is, the patterned bottom electrode 10 is located within the effective area of ​​the BAW resonator, and only the patterned top electrode 4 exists outside the effective area of ​​the BAW resonator, this embodiment can effectively avoid energy leakage caused by the piezoelectric effect between the patterned bottom electrode 10 located outside the effective area of ​​the BAW resonator and the top electrode located outside the effective area of ​​the BAW resonator. The prior art can prevent energy leakage by providing an air gap in the area outside the interconnection line of the top electrode, but providing an air gap will complicate the processing of the BAW resonator. Since the patterned bottom electrode 10 is not present in the area outside the interconnection line of the patterned top electrode 4 of this embodiment, this embodiment does not need to provide an air gap in the area outside the interconnection line of the patterned top electrode 4 to prevent energy leakage, thereby effectively simplifying the processing of the BAW resonator.

[0089] In some preferred embodiments, the second interconnect 7 is located at the edge of the patterned bottom electrode 10. Because the second interconnect 7 in this embodiment penetrates the piezoelectric layer 3 and is located at the edge of the patterned bottom electrode 1, this embodiment can effectively avoid the situation where the second interconnect 7 is located in the center of the BAW resonator, which would cause the structure of the piezoelectric layer 3 located in the center of the BAW resonator to be destroyed, thereby affecting the electrical performance of the BAW resonator. Preferably, the first interconnect 6 in this embodiment is located at the edge of the patterned top electrode 4 on a side away from the second interconnect 7.

[0090] In some preferred embodiments, there are multiple second interconnects 7. Since the second interconnects 7 in this embodiment penetrate the piezoelectric layer 3 and are made of metal, that is, the second interconnects 7 can dissipate heat generated by the BAW resonator during operation, this embodiment can increase the amount of heat dissipated per unit time by providing multiple second interconnects 7, thereby effectively enhancing the heat dissipation effect of the BAW resonator.

[0091] As can be seen from the above, the present application provides a high electrical performance bulk acoustic wave resonator, which utilizes a first substrate 1, a second interconnect line 7, a patterned bottom electrode 10 and a covering layer 11 to enclose a first air cavity 14, that is, the present application does not need to form a sacrificial layer and release the sacrificial layer on the substrate. Therefore, the present application can effectively solve the problem of tympaning or cracking of the bulk acoustic wave resonator film during the release of the sacrificial layer due to excessive stress or uneven stress distribution during the release of the sacrificial layer. Moreover, since the bottom electrode of the present application does not span the air cavity, the present application can also effectively solve the problem of partial energy leakage of the bulk acoustic wave resonator due to the generation of interference waves by the bottom electrode and the top electrode spanning the air cavity, thereby effectively improving the electrical performance of the bulk acoustic wave resonator.

[0092] Thirdly, as Figure 4-Figure 7 As shown, the present application also provides a bulk acoustic wave filter, which includes a plurality of high electrical performance bulk acoustic wave resonators provided by the second aspect above.

[0093] An embodiment of the present application provides a bulk acoustic wave filter, which includes a plurality of high-electrical-performance bulk acoustic wave resonators provided in the second aspect. The principle of the bulk acoustic wave filter provided by this embodiment is the same as the principle of the high-electrical-performance bulk acoustic wave resonator provided in the second aspect, and will not be discussed in detail here. It should be understood that the bulk acoustic wave filter of this embodiment includes a plurality of high-electrical-performance bulk acoustic wave resonators. This embodiment refers to two adjacent high-electrical-performance bulk acoustic wave resonators in the bulk acoustic wave filter as a first bulk acoustic wave resonator and a second bulk acoustic wave resonator. This embodiment can connect the patterned top electrode 4 of the first bulk acoustic wave resonator to the patterned bottom electrode 10 of the second bulk acoustic wave resonator by connecting the first interconnection line 6 of the first bulk acoustic wave resonator to the second interconnection line 7 of the second bulk acoustic wave resonator (refer to Figure 5 ), this embodiment can also connect the patterned top electrode 4 of the first BAW resonator to the patterned top electrode 4 of the second BAW resonator by connecting the first interconnection line 6 of the first BAW resonator to the first interconnection line 6 of the second BAW resonator (refer to Figure 6 ), this embodiment can also connect the patterned bottom electrode 10 of the first BAW resonator to the patterned bottom electrode 10 of the second BAW resonator by connecting the second interconnection line 7 of the first BAW resonator to the second interconnection line 7 of the second BAW resonator (refer to Figure 7 ).

[0094] From the above, it can be seen that the present application provides a high electrical performance bulk acoustic wave resonator, a preparation method and a bulk acoustic wave filter, which can form an acoustic reflector of the bulk acoustic wave resonator by first etching the first substrate 1, then forming a patterned bottom electrode 10 in the groove 9, and finally forming a coating layer 11 on the first substrate 1. That is, the present application does not need to form a sacrificial layer and release the sacrificial layer on the substrate. Therefore, the present application can effectively solve the problem of tympanic membrane or cracking of the bulk acoustic wave resonator film during the release of the sacrificial layer due to excessive stress or uneven stress distribution during the release of the sacrificial layer. Moreover, since the bottom electrode of the present application does not span the air cavity, the present application can also effectively solve the problem of partial energy leakage of the bulk acoustic wave resonator due to the generation of interference waves by the bottom electrode and the top electrode spanning the air cavity, thereby effectively improving the electrical performance of the bulk acoustic wave resonator.

[0095] In the embodiments provided in the present application, it should be understood that, in this document, relational terms such as first and second, etc., are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations.

[0096] The above description is merely an embodiment of the present application and is not intended to limit the scope of protection of the present application. For those skilled in the art, various modifications and variations of the present application are possible. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application shall be included in the scope of protection of the present application.

Claims

1. A method for preparing a bulk acoustic wave resonator with high electrical performance, characterized in that: The method for preparing a bulk acoustic wave resonator with high electrical performance comprises: S1. Forming a buffer layer, a piezoelectric layer, and a patterned top electrode in sequence on a first substrate, wherein the patterned top electrode partially covers the piezoelectric layer; S2, forming a blind hole outside the patterned top electrode, which penetrates the piezoelectric layer and the buffer layer and has a depth greater than 0 on the first substrate; S3, forming a first interconnection line on the top surface of the patterned top electrode and forming a second interconnection line on the top surface of the piezoelectric layer by filling the blind hole, wherein the second interconnection line is located outside the patterned top electrode; S4, bonding a second substrate on the first interconnection line and the second interconnection line to obtain an etched assembly, with a gap between the second substrate and the patterned top electrode; S5, turning the etching assembly upside down, and then etching the first substrate to form a groove on the first substrate to expose the buffer layer and the second interconnection line; S6, forming a patterned bottom electrode in the groove, the patterned bottom electrode being connected to the second interconnection line and having a top surface height smaller than a top surface height of the first substrate, and then mounting a cover film layer on the first substrate to form a bulk acoustic wave resonator; S7: remove the second substrate, then fix the BAW resonator on a packaging substrate through the first interconnection line and the second interconnection line, and perform plastic packaging on the BAW resonator.

2. The method for preparing a bulk acoustic wave resonator with high electrical performance according to claim 1, wherein: Step S1 includes: S11, forming a buffer layer on a first substrate; S12, depositing single-crystal aluminum nitride on the buffer layer based on a deposition process to form a piezoelectric layer on the buffer layer; S13, forming a patterned top electrode on the piezoelectric layer based on a deposition process and a patterning process.

3. The method for preparing a bulk acoustic wave resonator with high electrical performance according to claim 2, wherein: Step S1 also includes the following steps performed before step S11: S14, cleaning the first substrate.

4. The method for preparing a bulk acoustic wave resonator with high electrical performance according to claim 1, wherein: Step S5 includes: S51, turning the etching assembly upside down; S52, thinning the first substrate so that a distance between a top surface of the first substrate and a top surface of the second interconnection line is a preset distance; S53 . Etch the first substrate based on a dry etching process to form a groove on the first substrate to expose the buffer layer and the second interconnection line.

5. The method for preparing a bulk acoustic wave resonator with high electrical performance according to claim 1, wherein: The package substrate has a third interconnection line, and step S7 includes: S71, removing the second substrate based on a lift-off process; S72. Welding the first interconnection line, the second interconnection line, and the third interconnection line together based on a flip-chip process to fix the BAW resonator on the packaging substrate. S73 , performing plastic packaging on the BAW resonator based on a plastic packaging process.

6. A high electrical performance bulk acoustic wave resonator, characterized in that: The high-electrical-performance BAW resonator is manufactured by the method for preparing a high-electrical-performance BAW resonator according to any one of claims 1 to 5. The high-electrical-performance BAW resonator comprises a BAW resonator, a packaging substrate, and a plastic encapsulation layer. The BAW resonator comprises a first substrate, a buffer layer, a piezoelectric layer, a patterned top electrode, a first interconnect, a second interconnect, a patterned bottom electrode, a cover layer, and a first air cavity. The first interconnect is connected at both ends to the patterned top electrode and the packaging substrate, respectively. The second interconnect is connected to the piezoelectric layer and the packaging substrate. The second interconnect penetrates the piezoelectric layer and the buffer layer and has a depth greater than 0 on the first substrate. The patterned bottom electrode is connected to the buffer layer and the second interconnect. The first substrate is arranged around the patterned bottom electrode. The cover layer is connected to the top surface of the first substrate and has a gap between it and the patterned bottom electrode. The first air cavity is enclosed by the first substrate, the second interconnect, the patterned bottom electrode, and the cover layer. The plastic encapsulation layer is arranged on the packaging substrate and wraps around the outside of the BAW resonator.

7. The high electrical performance bulk acoustic wave resonator according to claim 6, characterized in that: The patterned bottom electrode and the patterned top electrode are arranged in a staggered manner.

8. The high electrical performance bulk acoustic wave resonator according to claim 6, characterized in that: The second interconnection line is located at an edge of the patterned bottom electrode.

9. The high electrical performance bulk acoustic wave resonator according to claim 6, characterized in that: There are multiple second interconnecting lines.

10. A bulk acoustic wave filter, characterized in that: The BAW filter comprises a plurality of BAW resonators with high electrical performance according to any one of claims 6 to 9.

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