Preparation method of a single-crystal piezoelectric thin-film bulk acoustic wave resonator

Abstract

The present invention provides a method for preparing a single-crystal piezoelectric thin-film bulk acoustic wave resonator, comprising: growing at least one layer of piezoelectric thin film on a first substrate; forming a first electrode; patterning the first electrode and the piezoelectric thin film, and then forming a bonding layer; etching the bonding layer to form a first opening; bonding and fixing the bonding layer to a second substrate, and the first opening forms a cavity structure; removing the first substrate to expose the bottom surface of the piezoelectric thin film, thinning the bottom surface of the piezoelectric thin film, and performing secondary piezoelectric thin film growth on the bottom surface of the piezoelectric thin film to form a secondary piezoelectric thin film growth layer; forming a dielectric layer, and patterning the dielectric layer to form a second opening; forming a second electrode, and fabricating an electrical lead-out structure. The present invention prepares a piezoelectric layer combining doped AlN and single-crystal AlN through a thinning and regrowth process, which is beneficial to improving the thickness and quality of the piezoelectric layer, improving the stress of the piezoelectric layer, and further enhancing performance parameters such as the electromechanical coupling coefficient and quality factor Q of the bulk acoustic wave resonator.

Description

Technical Field

[0001] The present invention belongs to the technical field of thin film bulk acoustic wave resonators, and particularly relates to a preparation method of a single crystal piezoelectric thin film bulk acoustic wave resonator. Background Art

[0002] At present, wireless data transmission requires radio frequency filters to have a working frequency of 5 GHz or higher. The filters applied in 5G communication are mainly bulk acoustic wave filters (BAW for short) and surface acoustic wave filters (SAW for short). BAW devices have extremely high Q values (above 4000), and the working frequency band ranges from 100 MHz to 20 GHz. They have the advantages of high working frequency, low insertion loss, high frequency selection characteristics, high power capacity, and strong anti-static ability, and are the best solutions for future radio frequency front-ends.

[0003] AlN materials have the advantages of high sound velocity, low loss, low temperature coefficient, etc., and are currently widely used in 4G filters. However, the piezoelectric coefficient and electromechanical coupling coefficient of polycrystalline AlN are small, which limits its application in 5G high-frequency broadband filters. Single crystal AlN devices can improve the effective electromechanical coupling coefficient of the device (depending on the electromechanical coupling coefficient of the piezoelectric layer), the quality factor Q value, and the power capacity. In addition, doping AlN with an appropriate concentration is also beneficial to improving the device performance, which is of great significance for realizing BAW devices with high electromechanical coupling coefficient and high Q value. There is still room for improvement in the film quality of existing AlN piezoelectric materials.

[0004] Therefore, providing a new preparation method of a single crystal piezoelectric thin film bulk acoustic wave resonator is a problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a preparation method of a single crystal piezoelectric thin film bulk acoustic wave resonator, which is used to solve the problem of low crystal quality of piezoelectric thin films in the prior art.

[0006] To achieve the above purpose and other related purposes, the present invention provides a preparation method of a single crystal piezoelectric thin film bulk acoustic wave resonator, and the preparation method at least includes:

[0007] 1) Provide a first substrate, and grow at least one layer of piezoelectric thin film on the first substrate;

[0008] 2) Form a first electrode on the surface of the piezoelectric thin film;

[0009] 3) Pattern the first electrode and the piezoelectric thin film, and form a bonding layer covering the first electrode and the piezoelectric thin film;

[0010] 4) Etch the bonding layer to form a first opening exposing the first electrode;

[0011] 5) Provide a second substrate, invert the structure obtained in step 4) so that the bonding layer is bonded and fixed to the second substrate, and the first opening forms a cavity structure;

[0012] 6) Remove the first substrate to expose the bottom surface of the piezoelectric thin film, thin the bottom surface of the piezoelectric thin film, and perform secondary piezoelectric thin film growth on the bottom surface of the piezoelectric thin film to form a secondary piezoelectric thin film growth layer;

[0013] 7) Form a dielectric layer on the surface of the secondary piezoelectric thin film growth layer and pattern the dielectric layer to form a second opening, and the projection of the second opening in the vertical direction falls within the cavity structure;

[0014] 8) Form a second electrode on the surface of the second opening and the dielectric layer, and fabricate an electrical lead-out structure for the first electrode and the second electrode.

[0015] Preferably, in step 1), a layer of piezoelectric thin film is grown on the first substrate, and the piezoelectric thin film is a single-crystalline aluminum nitride layer. Then, in step 6), the step of performing secondary piezoelectric thin film growth includes growing a doped aluminum nitride layer on the bottom surface of the piezoelectric thin film.

[0016] Preferably, in step 1), a layer of piezoelectric thin film is grown on the first substrate, and the piezoelectric thin film is a single-crystalline aluminum nitride layer. Then, in step 6), the step of performing secondary piezoelectric thin film growth includes: first growing another single-crystalline aluminum nitride layer on the bottom surface of the piezoelectric thin film, and then forming a doped aluminum nitride layer on the surface of the another single-crystalline aluminum nitride layer.

[0017] Preferably, in step 1), two layers of piezoelectric thin films are grown on the first substrate, and the piezoelectric thin films include a single-crystalline aluminum nitride layer and a doped aluminum nitride layer formed on the surface of the single-crystalline aluminum nitride layer. Then, in step 6), the step of performing secondary piezoelectric thin film growth includes growing another doped aluminum nitride layer on the bottom surface of the piezoelectric thin film.

[0018] Preferably, in step 1), three layers of piezoelectric thin films are grown on the first substrate, and the piezoelectric thin films include a single-crystalline aluminum nitride layer, a doped aluminum nitride layer, and another single-crystalline aluminum nitride layer grown in sequence. Then, in step 6), the step of performing secondary piezoelectric thin film growth includes growing another doped aluminum nitride layer on the bottom surface of the piezoelectric thin film.

[0019] Preferably, the single-crystal aluminum nitride layer is grown by a CVD process, the single-crystal aluminum nitride layer is grown by one of the processes of MOCVD, MBE, ALD, and PLD, and the doped aluminum nitride layer is grown by one of the processes of PVD, MBE, and MOCVD.

[0020] Preferably, the doping elements of the doped aluminum nitride layer include one or a combination of more of Sc, Y, Ta, and co-doping of Y / B.

[0021] Preferably, in step 6), the thinning thickness of the bottom surface of the piezoelectric thin film is between 10 nm and 100 nm.

[0022] Preferably, in step 6), the bottom surface of the piezoelectric thin film is thinned by an etching or chemical mechanical polishing process.

[0023] Preferably, in step 8), the steps of fabricating the electrical lead-out structures of the first electrode and the second electrode include:

[0024] Forming a through hole that penetrates the dielectric layer, the secondary piezoelectric thin film growth layer, and the piezoelectric thin film and exposes the surface of the first electrode, and depositing a first electrical lead-out structure communicating with the first electrode in the through hole;

[0025] Forming a second electrical lead-out structure communicating with the second electrode.

[0026] As described above, the preparation method of the single-crystal piezoelectric thin film bulk acoustic wave resonator of the present invention has the following beneficial effects:

[0027] 1. After removing the first substrate in the present invention, the bottom surface of the piezoelectric thin film is first thinned, and then a secondary piezoelectric thin film is grown on the bottom surface of the piezoelectric thin film to form a secondary piezoelectric thin film growth layer. In this step, the removed piezoelectric thin film with poor quality is first thinned, and then a secondary piezoelectric thin film growth layer with a predetermined thickness is deposited. In this way, while increasing the thickness of the piezoelectric thin film, the overall crystal quality of the piezoelectric thin film can be improved.

[0028] 2. The finally formed piezoelectric thin film layer of the present invention is a composite multi-layer film of single-crystal aluminum nitride and doped aluminum nitride. Compared with a single-layer single-crystal aluminum nitride layer, the composite multi-layer film of single-crystal aluminum nitride and doped aluminum nitride can increase the thickness and crystal quality of the piezoelectric layer and improve the device performance. Description of the Drawings

[0029] Figure 1 It is a schematic structural diagram presented in step 1) of the preparation method of the single-crystal piezoelectric thin film bulk acoustic wave resonator of the present invention.

[0030] Figure 2Schematic structural diagram presented in step 2) of the preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator of the present invention.

[0031] Figures 3 to 5 Schematic structural diagram presented in step 3) of the preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator of the present invention.

[0032] Figure 6 Schematic structural diagram presented in step 4) of the preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator of the present invention.

[0033] Figure 7 Schematic structural diagram presented in step 5) of the preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator of the present invention.

[0034] Figures 8 to 10 Schematic structural diagram presented in step 6) of the preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator of the present invention.

[0035] Figure 11 Schematic structural diagram presented in step 7) of the preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator of the present invention.

[0036] Figures 12 to 14 Schematic structural diagram presented in step 8) of the preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator of the present invention.

[0037] Figures 15 to 17 Schematic diagram of the composite layer formed by the piezoelectric thin film and the secondary piezoelectric thin film growth layer in each embodiment of the preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator of the present invention.

[0038] Description of component labels

[0039] 1 First substrate

[0040] 2 Piezoelectric thin film

[0041] 3 First electrode

[0042] 4 Bonding layer

[0043] 5 First opening

[0044] 6 Second substrate

[0045] 7 Secondary piezoelectric thin film growth layer

[0046] 8 Dielectric layer

[0047] 9 Second opening

[0048] 10 Second electrode

[0049] 11 Through hole

[0050] 12 First electrical lead-out structure

[0051] 13 Second electrical property lead-out structure Specific implementation manner

[0052] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0053] Please refer to the attached drawings. It should be noted that the drawings provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the drawings, rather than being drawn according to the number, shape, and size of the components during actual implementation. The type, quantity, and ratio of each component during its actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0054] As shown in Figures 1 to 14 the present invention provides a preparation method for a single-crystal piezoelectric thin-film bulk acoustic wave resonator. The preparation method at least includes the following steps:

[0055] First, perform step 1). As shown in Figure 1 provide a first substrate 1, and grow at least one layer of piezoelectric thin film 2 on the first substrate 1.

[0056] As an example, the material of the first substrate 1 includes but is not limited to materials such as single-crystalline silicon, silicon carbide, sapphire, or gallium nitride. In this embodiment, the first substrate 1 is preferably Si(111).

[0057] The piezoelectric thin film 2 formed in this step can be selected according to specific circumstances, and can be one layer, two layers, three layers, etc. As shown in Figure 15 and Figure 16 a single layer of piezoelectric thin film 2 is shown, Figure 17 and two layers of piezoelectric thin film 2 are shown. That is, the piezoelectric thin film 2 can be a single-crystalline aluminum nitride layer (AlN) grown once, or a multi-layer film combined with a single-crystalline aluminum nitride layer and a doped aluminum nitride layer grown multiple times.

[0058] Among them, the processes for growing the single-crystal aluminum nitride layer piezoelectric thin film 2 include but are not limited to MOCVD, MBE, ALD, PLD, etc. In this embodiment, MOCVD is preferably used. The processes for growing the doped aluminum nitride layer piezoelectric thin film 2 include but are not limited to magnetron sputtering (one of PVDs), MBE, MOCVD, etc. In this embodiment, the magnetron sputtering process is preferably used. As an example, the doped element in the doped aluminum nitride layer piezoelectric thin film 2 can be selected from one or a combination of Sc, Y, Ta, Y / B co-doping, etc., and Al is preferably used. 0.85 Sc 0.15 N.

[0059] Then perform step 2), as Figure 2 shown, form the first electrode 3 on the surface of the piezoelectric thin film 2.

[0060] As an example, the material of the first electrode 3 includes but is not limited to a combination of one or several of Mo, Pt, Al, Au, W, Ru. In this embodiment, the first electrode 3 is preferably Mo.

[0061] Next, perform step 3), as Figures 3 to 5 shown, pattern the first electrode 3 and the piezoelectric thin film 2, and form a bonding layer 4 covering the first electrode 3 and the piezoelectric thin film 2.

[0062] The processes for patterning the first electrode 3 and the piezoelectric thin film 2 include but are not limited to Lift-off, dry etching, or wet etching. As Figure 3 shown, after the patterning process, only the middle part of the first electrode 3 is retained. The shape of the patterned first electrode 3 includes but is not limited to regular or irregular shapes such as circles, ellipses, squares, polygons, duck-egg shapes, etc.

[0063] The step of forming the bonding layer 4 covering the first electrode 3 and the piezoelectric thin film 2 may include the following: Please refer to Figure 4 , first form the bonding layer 4 covering the first electrode 3 and the piezoelectric thin film 2, and this bonding layer 4 is thick and has an uneven surface; then please refer to Figure 5 , then planarize the surface of the bonding layer 4. For example, the surface of the bonding layer 4 can be planarized by means of chemical mechanical polishing (CMP), etc.

[0064] In this step, the bonding layer 4 can be deposited by chemical methods such as CVD, ALD, etc. In this embodiment, the deposition of the bonding layer 4 is preferably carried out by low-pressure LPCVD.

[0065] Next, perform step 4), as Figure 6 shown, etch the bonding layer 4 to form a first opening 5 exposing the first electrode 3.

[0066] The edge of the first opening 5 does not exceed the edge of the first electrode 3, that is, the projection of the first opening 5 on the surface of the piezoelectric thin film 2 is contained in the projection of the first electrode 3 on the surface of the piezoelectric thin film 2.

[0067] As an example, the first opening 5 can be formed by chemical vapor etching or physical etching.

[0068] Then, step 5) is performed. As Figure 7 shown, a second substrate 6 is provided, and the structure obtained in step 4) is inverted so that the bonding layer 4 is bonded and fixed to the second substrate 6, and the first opening 5 forms a cavity structure.

[0069] As an example, the second substrate 6 includes but is not limited to a single crystal silicon, silicon carbide, sapphire, or gallium nitride substrate. In this embodiment, the second substrate 6 is selected as a single crystal silicon.

[0070] The process of bonding and fixing the bonding layer 4 to the second substrate 6 includes steps such as pressurization, high-temperature strengthening, and annealing. Preferably, another bonding layer (not shown) can be deposited on the surface of the second substrate 6, and bonding between the two bonding layers can improve the success rate of bonding.

[0071] Then, step 6) is performed. As Figures 8 to 10 shown, the first substrate 1 is removed to expose the bottom surface of the piezoelectric thin film 2, the bottom surface of the piezoelectric thin film 2 is thinned, and secondary piezoelectric thin film growth is performed on the bottom surface of the piezoelectric thin film 2 to form a secondary piezoelectric thin film growth layer 7.

[0072] As an example, the method for removing the first substrate 1 includes but is not limited to ion implantation lift-off, mechanical grinding, polishing, wet etching, dry etching, and any combination of several of these methods.

[0073] It should be noted that after the structure obtained in step 4) is inverted, the piezoelectric thin film 2 is also flipped, and at this time, the bottom surface of the piezoelectric thin film 2 faces upward. Therefore, after the first substrate 1 is removed, the bottom surface of the piezoelectric thin film 2 is exposed.

[0074] In one embodiment, as Figure 15 shown, in step 1), only one layer of piezoelectric thin film 2 is grown on the first substrate 1, and the piezoelectric thin film 2 is a single crystal aluminum nitride layer (for convenience of illustration, Figure 15Only the piezoelectric thin film 2 of the single-crystal aluminum nitride layer is shown, and the first substrate 1 is not drawn. Then, in this step 6), the steps for growing the secondary piezoelectric thin film include growing a doped aluminum nitride layer (secondary piezoelectric thin film growth layer 7) on the bottom surface of the piezoelectric thin film 2. That is, in this step, after thinning the single-crystal aluminum nitride layer, a doped aluminum nitride layer is grown on the surface of the single-crystal aluminum nitride layer. Finally, a piezoelectric layer structure composed of a single-crystal aluminum nitride layer - doped aluminum nitride layer is formed.

[0075] In this embodiment, the piezoelectric thin film 2 in step 1) is a single-crystal aluminum nitride layer, and the growth thickness of this single-crystal aluminum nitride ranges between 50 nm and 300 nm, preferably 200 nm. The growth thickness of the doped aluminum nitride layer for growing the secondary piezoelectric thin film in step 6) ranges between 100 nm and 500 nm, preferably 300 nm.

[0076] In another embodiment, as Figure 16 shown, when growing the secondary piezoelectric thin film, an additional single-crystal aluminum nitride layer can be grown on the basis of the previous embodiment. Then, the steps for growing the secondary piezoelectric thin film in this step include: first growing another single-crystal aluminum nitride layer on the bottom surface of the piezoelectric thin film 2, and then forming a doped aluminum nitride layer on the surface of the another single-crystal aluminum nitride layer. That is, in this step, after thinning the single-crystal aluminum nitride layer (piezoelectric thin film 2), a single-crystal aluminum nitride layer and a doped aluminum nitride layer (secondary piezoelectric thin film growth layer 7) are sequentially grown on the surface of the single-crystal aluminum nitride layer. Finally, a piezoelectric layer structure composed of a single-crystal aluminum nitride layer - doped aluminum nitride layer is formed.

[0077] In this embodiment, the piezoelectric thin film 2 in step 1) is a single-crystal aluminum nitride layer, and the growth thickness of this single-crystal aluminum nitride ranges between 50 nm and 300 nm, preferably 100 nm. The growth thickness of the doped aluminum nitride layer for growing the secondary piezoelectric thin film in step 6) ranges between 100 nm and 500 nm, preferably 300 nm, and the growth thickness of the single-crystal aluminum nitride layer for growing the secondary piezoelectric thin film ranges between 50 nm and 500 nm, preferably 100 nm.

[0078] In yet another embodiment, as Figure 17As shown, in step 1), two layers of piezoelectric thin films are grown on the first substrate 1. The piezoelectric thin film 2 includes a single-crystalline aluminum nitride layer and a doped aluminum nitride layer formed on the surface of the single-crystalline aluminum nitride layer. Then, in this step 6), the step of growing the secondary piezoelectric thin film includes growing another doped aluminum nitride layer (secondary piezoelectric thin film growth layer 7) on the bottom surface of the piezoelectric thin film 2. It should be noted that after the inversion in step 4), the single-crystalline aluminum nitride layer in the piezoelectric thin film 2 is on the top and the doped aluminum nitride layer is on the bottom. After thinning the single-crystalline aluminum nitride layer on the top, another layer of doped aluminum nitride layer (secondary piezoelectric thin film growth layer 7) is grown on the surface of the single-crystalline aluminum nitride layer. Finally, a sandwich piezoelectric layer structure composed of a doped aluminum nitride layer - single-crystalline aluminum nitride layer - doped aluminum nitride layer is formed.

[0079] In this embodiment, the piezoelectric thin film 2 in step 1) is a combination of a single-crystalline aluminum nitride layer and a doped aluminum nitride layer. The growth thickness of the single-crystalline aluminum nitride ranges between 50 nm and 300 nm, preferably 200 nm. The growth thickness of the doped aluminum nitride ranges between 100 and 500 nm, preferably 150 nm. In step 6), the growth thickness of the doped aluminum nitride layer for the secondary piezoelectric thin film growth ranges between 100 nm and 500 nm, preferably 150 nm.

[0080] It should also be noted that the growth process of the piezoelectric thin film and the secondary piezoelectric thin film in the present invention mainly involves growing a doped aluminum nitride layer on the surface of the single-crystalline aluminum nitride layer, or growing another single-crystalline aluminum nitride layer on the surface of a thinner single-crystalline aluminum nitride layer, avoiding the process of growing a single-crystalline aluminum nitride layer on the surface of the doped aluminum nitride layer. In this way, the overall quality of the grown piezoelectric layer is better.

[0081] As an example, in the process of growing the secondary piezoelectric thin film, the process of growing the single-crystalline aluminum nitride layer includes but is not limited to MOCVD, MBE, ALD, PLD, etc. In this embodiment, MOCVD is preferably used. The process of growing the doped aluminum nitride layer includes but is not limited to processes such as magnetron sputtering, MBE, MOCVD, etc. In this embodiment, the magnetron sputtering process is preferably used. As an example, the doped element can be selected from one or a combination of Sc, Y, Ta, Y / B co-doping, etc., and Al is preferably used. 0.85 Sc 0.15 N.

[0082] The thinning thickness of the bottom surface of the piezoelectric thin film 2 is determined according to the growth quality of the piezoelectric thin film grown in step 1). As an example, the thinning thickness of the bottom surface of the piezoelectric thin film 2 ranges from 10 nm to 100 nm. For example, it can be 10 nm, 20 nm, 50 nm, 80 nm, 100 nm, etc. Specifically, the piezoelectric thin film with poor quality on the top layer (the bottom surface of the piezoelectric thin film 2 facing upward after inversion) can be removed by etching or polishing processes. For example, when the part with poor quality of the single-crystal aluminum nitride layer is removed, the subsequent second-grown piezoelectric thin film growth layer has a better crystal orientation and fewer defects. Therefore, through the thinning and regrowth processes, on the one hand, the overall thickness of the piezoelectric thin film can be increased, and on the other hand, the crystal quality of the overall piezoelectric thin film can be improved.

[0083] Then perform step 7). As Figure 11 shown, a dielectric layer 8 is formed on the surface of the secondary piezoelectric thin film growth layer 7, and the dielectric layer 8 is patterned to form a second opening 9, and the projection of the second opening 9 in the vertical direction falls into the cavity structure.

[0084] As an example, the optional materials for forming the dielectric layer 8 include but are not limited to silicon dioxide, silicon nitride, aluminum oxide, and aluminum nitride, and preferably silicon dioxide.

[0085] As an example, the methods for forming the second opening 9 include but are not limited to dry or wet etching.

[0086] Finally, perform step 8). As Figure 12 shown, a second electrode 10 is formed on the surface of the second opening 9 and the dielectric layer 8, as Figures 13 to 14 shown, and an electrical lead-out structure for the first electrode 3 and the second electrode 10 is fabricated.

[0087] As an example, the materials for the second electrode 10 include but are not limited to one or a combination of Mo, Pt, Al, Au, W, and Ru. In this embodiment, the second electrode is preferably Mo.

[0088] As an example, the steps for fabricating the electrical lead-out structure for the first electrode 3 and the second electrode 10 include: Please refer to Figure 13 , a through hole 11 is formed that penetrates the dielectric layer 8, the secondary piezoelectric thin film growth layer 7, and the piezoelectric thin film 2 and exposes the surface of the first electrode 3. As Figure 14 shown, a first electrical lead-out structure 12 communicating with the first electrode 3 is deposited in the through hole 11; then a second electrical lead-out structure 13 communicating with the second electrode 10 is formed.

[0089] As an example, the through hole 11 can be formed by dry or wet etching, and preferably the through hole 11 is formed by ICP dry etching.

[0090] As an example, the materials of the first electrical lead-out structure 12 and the second electrical lead-out structure 13 include, but are not limited to, one or a combination of several of metals or metalloids such as Ti, Al, Au, Cu, or TiN, and a combination of Ti and Au is preferred. The formation processes of the first electrical lead-out structure 12 and the second electrical lead-out structure 13 include thin-film deposition and patterning processes.

[0091] So far, the preparation of the single-crystal piezoelectric thin-film bulk acoustic wave resonator is completed. In the obtained single-crystal piezoelectric thin-film bulk acoustic wave resonator, its piezoelectric layer not only has a single-crystal aluminum nitride layer, but also includes a doped aluminum nitride layer. Such a piezoelectric combined layer can improve the quality and thickness of the piezoelectric layer, and can improve stress, further enhancing the electromechanical coupling coefficient K t 2 of the bulk acoustic wave resonator, the quality factor Q, etc.

[0092] In summary, the present invention provides a method for preparing a single-crystal piezoelectric thin-film bulk acoustic wave resonator, and the method includes: growing at least one piezoelectric thin film on a first substrate; forming a first electrode; patterning the first electrode and the piezoelectric thin film, and then forming a bonding layer; etching the bonding layer to form a first opening; bonding and fixing the bonding layer to a second substrate, and the first opening forms a cavity structure; removing the first substrate to expose the bottom surface of the piezoelectric thin film, thinning the bottom surface of the piezoelectric thin film, and performing secondary piezoelectric thin film growth on the bottom surface of the piezoelectric thin film to form a secondary piezoelectric thin film growth layer; forming a dielectric layer, and patterning the dielectric layer to form a second opening; forming a second electrode, and fabricating an electrical lead-out structure. The present invention prepares a piezoelectric layer combining doped AlN and single-crystal AlN through thinning and regrowth processes, which is beneficial to improving the thickness and quality of the piezoelectric layer, improving the stress of the piezoelectric layer, and further enhancing performance parameters such as the electromechanical coupling coefficient and the quality factor Q of the bulk acoustic wave resonator.

[0093] Therefore, the present invention effectively overcomes various drawbacks in the prior art and has high industrial utilization value.

[0094] The above embodiments are only illustrative of the principles and effects of the present invention, and are not used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical idea disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A preparation method of a single-crystal piezoelectric thin-film bulk acoustic wave resonator, characterized in that The preparation method at least includes: 1) Providing a first substrate and growing at least one layer of piezoelectric thin film on the first substrate; 2) Forming a first electrode on the surface of the piezoelectric thin film; 3) Patterning the first electrode and the piezoelectric thin film and forming a bonding layer covering the first electrode and the piezoelectric thin film; 4) Etching the bonding layer to form a first opening exposing the first electrode; 5) Providing a second substrate, inverting the structure obtained in step 4) so that the bonding layer is bonded and fixed to the second substrate, and the first opening forms a cavity structure; 6) Removing the first substrate to expose the bottom surface of the piezoelectric thin film, thinning the bottom surface of the piezoelectric thin film, and performing secondary piezoelectric thin film growth on the bottom surface of the piezoelectric thin film to form a secondary piezoelectric thin film growth layer; 7) Forming a dielectric layer on the surface of the secondary piezoelectric thin film growth layer and patterning the dielectric layer to form a second opening, and the projection of the second opening in the vertical direction falls into the cavity structure; 8) Forming a second electrode on the surface of the second opening and the dielectric layer and fabricating an electrical lead-out structure for the first electrode and the second electrode; In step 1), if one layer of piezoelectric thin film is grown on the first substrate and the piezoelectric thin film is a single-crystalline aluminum nitride layer, then in step 6), the steps for performing secondary piezoelectric thin film growth include: first growing another single-crystalline aluminum nitride layer on the bottom surface of the piezoelectric thin film, and then forming a doped aluminum nitride layer on the surface of the another single-crystalline aluminum nitride layer; or: In step 1), if two layers of piezoelectric thin films are grown on the first substrate and the piezoelectric thin films include a single-crystalline aluminum nitride layer and a doped aluminum nitride layer formed on the surface of the single-crystalline aluminum nitride layer, then in step 6), the steps for performing secondary piezoelectric thin film growth include growing another doped aluminum nitride layer on the bottom surface of the piezoelectric thin film.

2. The preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator according to any one of claim 1, characterized in that: Using one of the processes of MOCVD, MBE, ALD, and PLD to grow the single-crystalline aluminum nitride layer, and using one of the processes of PVD, MBE, and MOCVD to grow the doped aluminum nitride layer.

3. The preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator according to any one of claims 1, wherein: The doping elements of the doped aluminum nitride layer include one or a combination of more of Sc, Y, Ta, and Y / B co-doping.

4. The preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator according to claim 1, characterized in that: In step 6), the thinning thickness of the bottom surface of the piezoelectric thin film is between 10 nm and 100 nm.

5. The preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator according to claim 1, wherein: In step 6), the bottom surface of the piezoelectric thin film is thinned by an etching or chemical mechanical polishing process.

6. The preparation method of the single-crystal piezoelectric thin-film bulk acoustic wave resonator according to claim 1, characterized in that: In step 8), the steps for fabricating the electrical lead-out structure for the first electrode and the second electrode include: Forming a through hole that penetrates the dielectric layer, the secondary piezoelectric thin film growth layer, and the piezoelectric thin film and exposes the surface of the first electrode, and depositing a first electrical lead-out structure connected to the first electrode in the through hole; Forming a second electrical lead-out structure connected to the second electrode.

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