Bulk acoustic wave resonator and manufacturing method therefor, and electronic device

Abstract

The present disclosure relates to the technical field of radio frequency, and provides a bulk acoustic wave resonator and a manufacturing method therefor, and an electronic device. The bulk acoustic wave resonator of the present disclosure comprises: a base substrate, a first electrode, a piezoelectric layer, and a second electrode; the first electrode is arranged on the base substrate, the second electrode is arranged on the side of the first electrode facing away from the base substrate, the piezoelectric layer is arranged between the first electrode and the second electrode, and the orthographic projections of any two of the first electrode, the piezoelectric layer, and the second electrode on the base substrate at least partially overlap; the bulk acoustic wave resonator is divided into a working area and a peripheral area surrounding the working area; and the bulk acoustic wave resonator comprises a first air gap located in the peripheral area, and the first air gap at least passes through part of the thickness of the piezoelectric layer in the direction perpendicular to the base substrate.

Description

Bulk acoustic wave resonator, preparation method thereof, and electronic device Technical Field

[0001] The present disclosure belongs to the field of radio frequency technology, and particularly relates to a bulk acoustic wave resonator, a preparation method thereof, and an electronic device. Background Art

[0002] In the field of mobile communications, because the total available frequency range is relatively narrow and there are many frequency bands used for mobile communications, the spacing between adjacent frequency bands is very narrow (approximately a few MHz to tens of MHz), and the bandwidth of a single frequency band is very narrow (tens of MHz), the filters used in mobile phones must have the performance characteristics of small in-band ripple, large out-of-band suppression, and good rectangularity. Conventional microstrip filters are large in size, have insufficient out-of-band suppression, and poor rectangularity, making them unsuitable. Cavity filters are also large in size and cannot be matched. Dielectric filters have large in-band insertion loss and poor rectangularity, making them unsuitable. IPD filters have large in-band ripple and poor rectangularity, making them unsuitable.

[0003] BAW resonators, the basic structural unit of BAW filters, currently use a silicon wafer as the substrate material, with a sandwich structure consisting of a first electrode, a piezoelectric material, and a second electrode from bottom to top. The operating principle is that a radio frequency signal is transmitted through the electrode at one end of the resonator. It is then converted into a mechanical vibration acoustic wave signal through the inverse piezoelectric effect at the interface between the piezoelectric material and the metal electrode. This acoustic wave signal forms a resonant standing wave with a certain frequency in the sandwich structure of the first electrode, piezoelectric material, and second electrode. The frequency of the radio frequency signal is equal to the resonant frequency of the resonator. The acoustic wave signal is then transmitted to the electrode at the other end of the resonator, where it is converted into a radio frequency signal through the piezoelectric effect at the interface between the metal electrode and the piezoelectric material. The resonator has a fixed resonant frequency. When the frequency of the RF signal is equal to the resonant frequency of the resonator, the conversion efficiency of RF signal → acoustic wave signal → RF signal is high; when the frequency of the RF signal is not equal to the resonant frequency of the resonator, the conversion efficiency of RF signal → acoustic wave signal → RF signal is very low, and most of the RF signals cannot be transmitted from the resonator. That is, the resonator is equivalent to the function of a filter to filter the RF signal.

[0004] Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art and provides a bulk acoustic wave resonator, a preparation method thereof, and an electronic device.

[0006] An embodiment of the present disclosure provides a bulk acoustic wave resonator, comprising: a substrate, a first electrode, a piezoelectric layer, and a second electrode; the first electrode is disposed on the substrate, the second electrode is disposed on a side of the first electrode facing away from the substrate, the piezoelectric layer is disposed between the first electrode and the second electrode, and the orthographic projections of any two of the first electrode, the piezoelectric layer, and the second electrode on the substrate at least partially overlap; wherein,

[0007] The BAW resonator is divided into a working area and a peripheral area surrounding the working area; the BAW resonator includes a first air gap located in the peripheral area, and the first air gap penetrates at least part of the thickness of the piezoelectric layer along a direction perpendicular to the substrate.

[0008] The first air gap penetrates the piezoelectric layer in a direction perpendicular to the substrate.

[0009] The first air gap penetrates the piezoelectric layer and the first electrode in a direction perpendicular to the substrate.

[0010] The second electrode includes a main body located in the working area and an edge portion located in the peripheral area and connected to the main body. The main body contacts the piezoelectric layer, and a certain gap exists between the edge portion and the piezoelectric layer to form a second air gap.

[0011] The first air gap and the orthographic projection of the edge portion on the plane where the base substrate is located do not overlap.

[0012] The first air gap overlaps with the orthographic projection of the edge portion on the plane where the base substrate is located.

[0013] The orthographic projection of the first air gap on the plane where the substrate is located is annular.

[0014] The first air gap includes a plurality of spaced sub-air gaps surrounding the working area.

[0015] In which, the base substrate has a first cavity extending through the substrate along its thickness direction; the base substrate includes a first surface and a second surface arranged opposite to each other along its thickness direction; the first cavity includes a first opening and a second opening arranged opposite to each other; the first opening is located on the first surface, and the second opening is located on the second surface; the first electrode covers the first opening.

[0016] In which, the base substrate has a first groove portion; the base substrate includes a first surface and a second surface arranged opposite to each other along its thickness direction; the first groove portion includes a third opening, and the third opening is located on the first surface; the first electrode is located on the first surface; the outline of the positive projection of the third opening on the second surface is within the outline of the positive projection of the first electrode on the second surface.

[0017] Wherein, a support layer is provided between the first surface of the base substrate and the first electrode.

[0018] Wherein, the BAW resonator further includes a support layer arranged between the base substrate and the first electrode; a certain space is defined between the support layer and the base substrate.

[0019] In which, the bulk acoustic wave resonator also includes at least one layer of reflector structure arranged between the first electrode and the base substrate; the reflector structure includes a first substructure layer and a second substructure layer arranged in sequence along a direction away from the base substrate, and the acoustic impedance of the material of the first substructure layer is greater than the acoustic impedance of the material of the second substructure layer.

[0020] The first air gap penetrates the piezoelectric layer, the first electrode, and the second substructure layer closest to the first electrode.

[0021] The BAW resonator further includes a mass load layer provided on a side of the second electrode facing away from the substrate.

[0022] An embodiment of the present disclosure provides a method for fabricating a bulk acoustic wave resonator, comprising: sequentially forming a first electrode, a piezoelectric layer, and a second electrode on a substrate, wherein the orthographic projections of any two of the first electrode, the piezoelectric layer, and the second electrode on the substrate at least partially overlap; wherein the bulk acoustic wave resonator is divided into an active area and a peripheral area surrounding the active area;

[0023] The preparation method further includes: forming a first air gap in the peripheral area; the first air gap penetrates at least a portion of the thickness of the piezoelectric layer in a direction perpendicular to the substrate.

[0024] The first air gap penetrates the piezoelectric layer in a direction perpendicular to the substrate.

[0025] The first air gap penetrates the piezoelectric layer and the first electrode in a direction perpendicular to the substrate.

[0026] The preparation method further comprises: after forming the piezoelectric layer, forming a second sacrificial layer in a peripheral area of ​​the piezoelectric layer;

[0027] The second electrode is formed on the side of the second sacrificial layer and the piezoelectric layer facing away from the base substrate; after the second electrode is formed, the second sacrificial layer is etched away so that the second electrode includes a main body located in the working area, and an edge portion located in the peripheral area and connected to the main body, the main body is in contact with the piezoelectric layer, and the edge portion has a certain gap with the piezoelectric layer to form a second air gap.

[0028] The orthographic projection of the first air gap on the plane where the substrate is located is annular.

[0029] The first air gap includes a plurality of spaced sub-air gaps surrounding the working area.

[0030] Among them, the preparation method also includes: processing the base substrate to form a first cavity that penetrates along the thickness direction of the base substrate; the base substrate includes a first surface and a second surface that are oppositely arranged along its thickness direction; the first cavity includes a first opening and a second opening that are oppositely arranged; the first opening is located on the first surface, and the second opening is located on the second surface; the first electrode covers the first opening.

[0031] Among them, the preparation method also includes: processing the base substrate to form a first groove portion; the base substrate includes a first surface and a second surface arranged opposite to each other along its thickness direction; the first groove portion includes a third opening, and the third opening is located on the first surface; the first electrode is located on the first surface; the outline of the positive projection of the third opening on the second surface is within the outline of the positive projection of the first electrode on the second surface.

[0032] Wherein, the preparation method further comprises:

[0033] forming a first sacrificial layer in the first groove;

[0034] A support layer is formed on a side of the first groove away from the base substrate; and the first electrode is formed on a side of the support layer away from the base substrate.

[0035] A first through hole is formed through the first electrode and the support layer, and the first sacrificial layer is removed by etching through the first through hole.

[0036] Wherein, the preparation method further comprises:

[0037] forming a first sacrificial layer on the base substrate;

[0038] forming a supporting layer on a side of the first sacrificial layer away from the base substrate; and forming the first electrode on a side of the supporting layer away from the base substrate;

[0039] A first through hole is formed through the first electrode and the support layer, and the first sacrificial layer is removed by etching through the first through hole.

[0040] Before forming the first electrode, the method further includes:

[0041] At least one reflector structure is formed on the base substrate; the reflector structure includes a first substructure layer and a second substructure layer formed in sequence along a direction away from the base substrate, and the acoustic impedance of the material of the first substructure layer is greater than the acoustic impedance of the material of the second substructure layer.

[0042] The first air gap penetrates the piezoelectric layer, the first electrode, and the second substructure layer closest to the first electrode.

[0043] Wherein, the preparation method further comprises forming a mass load layer on the side of the second electrode away from the base substrate.

[0044] An embodiment of the present disclosure provides an electronic device, comprising any of the above-mentioned bulk acoustic wave resonators. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] FIG1 is a schematic structural diagram of a back-etched bulk acoustic wave resonator.

[0046] FIG2 is a schematic structural diagram of a thin film bulk acoustic wave resonator.

[0047] FIG3 is a schematic structural diagram of another thin film bulk acoustic wave resonator.

[0048] FIG4 is a schematic structural diagram of a solid-state assembled bulk acoustic wave resonator.

[0049] FIG5 is a schematic diagram of a bulk acoustic wave resonator according to a first example of an embodiment of the present disclosure.

[0050] FIG6 is a schematic diagram of another BAW resonator according to the first example of the present disclosure.

[0051] FIG. 7 is a schematic diagram of yet another BAW resonator according to the first example of the present disclosure.

[0052] FIG8 is a schematic diagram of yet another BAW resonator according to the first example of the present disclosure.

[0053] FIG9 is a flow chart of the preparation process of the BAW resonator shown in FIG7 .

[0054] FIG10 is a schematic diagram of a bulk acoustic wave resonator according to a second example of an embodiment of the present disclosure.

[0055] FIG11 is a schematic diagram of another BAW resonator according to a second example of an embodiment of the present disclosure.

[0056] FIG12 is a schematic diagram of yet another BAW resonator according to a second example of an embodiment of the present disclosure.

[0057] FIG. 13 is a flow chart of the preparation process of the BAW resonator shown in FIG. 10 .

[0058] FIG. 14 is a schematic diagram of a third exemplary BAW resonator according to an embodiment of the present disclosure.

[0059] FIG. 15 is a flow chart of the preparation process of the BAW resonator shown in FIG. 14 .

[0060] FIG16 is a schematic diagram of a bulk acoustic wave resonator according to a fourth example of an embodiment of the present disclosure.

[0061] FIG. 17 is a schematic diagram of another BAW resonator according to a fourth example of an embodiment of the present disclosure.

[0062] FIG18 is a flow chart of the preparation process of the BAW resonator shown in FIG16 . DETAILED DESCRIPTION

[0063] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0064] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the usual meanings understood by people with ordinary skills in the field to which this disclosure belongs. The words "first", "second" and similar words used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one", "an" or "the" do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0065] As shown in Figures 1-4, in order to reduce insertion loss during filtering, a bulk acoustic wave resonator needs to confine the acoustic wave signal as much as possible within the piezoelectric layer 12 between the first electrode and the second electrode 13 to prevent the acoustic wave signal from spreading outward. Therefore, acoustic wave reflectors are usually constructed on the upper and lower surfaces of the resonator. The upper surface generally uses a low-acoustic-impedance air medium as a reflector. Depending on the construction of the acoustic wave reflector on the lower surface, bulk acoustic wave resonators are divided into three major categories: back-etched bulk acoustic wave resonators, as shown in Figure 1; film bulk acoustic resonators (abbreviated as FBAR), thin-film bulk acoustic wave resonators, as shown in Figures 2 and 3; and solid mounted resonators (abbreviated as SMR), solid-state assembly bulk acoustic wave resonators, as shown in Figure 4. Among them, FBAR is constructed with a first groove 102 etched on the substrate below the first electrode as an air gap, and then the first electrode is supported by a support layer 14, as shown in Figure 2a. Alternatively, a first groove 102 is formed through the support layer 14 as an air gap, as shown in Figure 2b. The SMR method constructs an acoustic reflector structure 15 below the first electrode, which is formed by alternating and repeating high acoustic impedance layers 151 and low acoustic impedance material layers 152. The back-etch type constructs a first cavity 101 formed on the substrate below the first electrode as an air layer by deeply etching the back side of the silicon substrate to form a cavity.

[0066] In existing BAW resonators, to reduce insertion loss during filtering, the acoustic signal needs to be confined as much as possible within the piezoelectric material (i.e., the piezoelectric layer) to prevent it from spreading outward. Therefore, acoustic reflectors are typically constructed on the upper and lower surfaces of the resonator. To reduce lateral acoustic loss, the following technical solutions are provided in the disclosed embodiments.

[0067] First example: FIG5 is a schematic diagram of a bulk acoustic wave resonator of the first example implemented in the present disclosure; as shown in FIG5 , the bulk acoustic wave resonator is divided into a working area Q1 and a peripheral area Q2 surrounding the working area Q1, and the bulk acoustic wave resonator includes a base substrate 10, and a support layer 14, a first electrode 11, a piezoelectric layer 12, and a second electrode 13 sequentially arranged on the base substrate 10. A certain space is defined between the support layer 14 and the base substrate 10 to form a first groove 102 (air gap). The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the base substrate 10 at least partially overlap. Specifically, in the working area Q1, the first electrode 11 and the second electrode 13 are respectively attached to the upper and lower surfaces of the piezoelectric layer 12, and in the peripheral area Q2, a first air gap 41 is provided that passes through at least part of the thickness of the piezoelectric layer 12 in a direction perpendicular to the base substrate 10.

[0068] In some examples, the first air gap 41 may completely penetrate the piezoelectric layer 12 or only partially penetrate the thickness of the piezoelectric layer 12. FIG6 is a schematic diagram of another BAW resonator according to the first example of the present disclosure. As shown in FIG6 , the first air gap 41 may also penetrate the piezoelectric layer 12 and the first electrode 11. In this example, the first air gap 41 penetrating the piezoelectric layer 12 and the first electrode 11 is used as an example.

[0069] 5 , the input RF signal is converted into an acoustic wave signal through the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, and propagates longitudinally in the piezoelectric layer 12. When it reaches the interface between the first electrode 11 and the piezoelectric layer 12, it is converted into an RF signal through the piezoelectric effect and then propagates out. The air gap below the resonator and the air layer above the resonator act as acoustic reflectors, and their function is to confine the acoustic signal within the resonator structure rather than dissipate it, thereby reducing the loss of the resonator. At the same time, in the peripheral area Q2, the piezoelectric layer 12 and the first electrode 11 below are interrupted to form a first air gap 41, that is, a longitudinal air wall structure is formed, so that the acoustic waves propagating laterally near the piezoelectric layer 12 and the first electrode 11 are fully reflected at the air wall structure and return to the piezoelectric resonator instead of propagating outward and dissipating, thereby reducing the loss of the device. Of course, if the first air gap 41 only penetrates part of the thickness of the piezoelectric layer 12 or completely penetrates the piezoelectric layer 12, the longitudinal air wall structure formed can also cause the sound waves propagating laterally inside the piezoelectric layer 12 to be totally reflected at the wall structure and return to the piezoelectric resonator instead of propagating outward and dissipating, thereby reducing the loss of the device.

[0070] In some examples, FIG7 is a schematic diagram of another BAW resonator of the first example implemented in the present disclosure; as shown in FIG7 , the BAW resonator includes not only the above-mentioned structure, but also includes a second air gap 42 defined by the piezoelectric layer 12 and the second electrode 13 in the peripheral region Q2. Specifically, the second electrode 13 includes a main body portion and an edge portion connected to the main body portion, wherein the main body portion is located in the working region Q1, the edge portion is located in the peripheral region Q2, the main body portion is in contact with the piezoelectric layer 12, and the edge portion has a certain gap with the piezoelectric layer 12, forming a second air gap 42. The second air gap 42 can make the sound waves propagating laterally inside the piezoelectric layer 12 be fully reflected at the wall structure and return to the piezoelectric resonator instead of propagating outward and dissipating, thereby reducing the loss of the device.

[0071] In some examples, a mass load layer 16 may be further provided on the side of the second electrode 13 facing away from the base substrate 10. On the one hand, the film layer can isolate water vapor and oxygen, act as a package, and prevent the performance of the piezoelectric resonator from deteriorating over time. On the other hand, when the frequency of the piezoelectric resonator shifts, the frequency of the piezoelectric resonator can be adjusted and corrected to an ideal value by performing local plasma etching on the mass load layer 16.

[0072] The mass-loading layer 16 is preferably made of inorganic materials such as SiNx, Al2O3, SiO2, AlN, and BN, which can isolate water vapor and oxygen. Alternatively, various metal materials (such as Mo, Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, and Se, or alloys of various metals or stacks of various metal layers) or organic compounds such as polyimide and epoxy resin may be selected. The mass-loading layer 16 may be a single layer of a single material or a stack of multiple materials.

[0073] In some examples, the base substrate 10 is preferably Si, and materials such as glass, sapphire, SiC, GaAs, GaN, InP, BN, and ZnO may also be selected. The thickness of the base substrate 10 ranges from 0.1 um to 10 mm.

[0074] In some examples, the first electrode 11 is preferably made of molybdenum. Alternatively, materials such as Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, or Se may be used. Alternatively, an alloy of the above metals or a stack of metal layers may be used. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0075] In some examples, the piezoelectric layer 12 is preferably AlN, followed by Sc-doped AlN, and may also be BN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. It can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0076] In some examples, the second electrode 13 is preferably made of molybdenum. Other materials include Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, and Se. An alloy of the above metals or a stack of metal layers may also be used. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0077] In some examples, the support layer 14 is preferably made of electrically insulating Si3N4, but may also be made of SiO2, Al2O3, AlN, BN, etc. It may be a single material or a stack of the above materials. The thickness of the support layer 14 ranges from 1 nm to 10 μm.

[0078] In addition, since the support layer 14 and the base substrate 10 form a space, that is, an air gap sound reflection layer structure. During preparation, a first sacrificial layer 61 can be formed on the base substrate 10, and the support layer 14 covers the first sacrificial layer 61. After forming the second electrode 13 layer, a release hole is formed in the peripheral area Q2 that passes through the first electrode 11 and the piezoelectric layer 12. The first sacrificial layer 61 is released through the release hole, and then an air gap sound reflection layer structure is formed. Among them, the material of the first sacrificial layer 61 is preferably loose silicon dioxide doped with boron and phosphorus, or boron-doped loose silicon dioxide, or phosphorus-doped loose silicon dioxide. SiO2, SiN x , Al2O3, thickness range is 1nm to 100um.

[0079] In some examples, FIG8 is a schematic diagram of another BAW resonator according to the first example of the present disclosure. As shown in FIG8 , an air gap acoustic reflection layer structure can also be formed on a base substrate 10. In this case, a first groove 102 is formed on the first substrate, and a support layer 14 is formed on the first groove 102. The base substrate 10 includes a first surface and a second surface disposed opposite each other along its thickness direction. The first groove 102 includes a third opening, which is located on the first surface. The first electrode 11 is located on the first surface. The contour of the orthographic projection of the third opening on the second surface is within the contour of the orthographic projection of the first electrode 11 on the second surface. The remaining structure is the same as that of the BAW resonator described above and will not be described in detail here.

[0080] In this example, a method for preparing a BAW resonator is provided, taking the BAW resonator shown in FIG7 as an example. FIG9 is a flow chart of preparing the BAW resonator shown in FIG7 . As shown in FIG9 , the method specifically includes the following steps:

[0081] S11, providing a base substrate 10.

[0082] In this step, the base substrate 10 may be cleaned and then dried by an air knife.

[0083] S12 , forming a first sacrificial layer 61 on the base substrate 10 .

[0084] In some examples, step S12 may include first depositing a first sacrificial layer 61, preferably plasma enhanced chemical vapor deposition (PECVD), and alternatively low pressure chemical vapor deposition (LPCVD), radio frequency magnetron sputtering, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), thermal evaporation, or electron beam evaporation. The first sacrificial layer 61 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, and alternatively a dry etching process is selected to form a pattern of the first sacrificial layer 61.

[0085] S13 , forming a support layer 14 on the first sacrificial layer 61 , wherein the support layer 14 covers the first sacrificial layer 61 .

[0086] In some examples, step S13 may include first depositing the entire surface of the electrically insulating material, where the deposition method may include radio frequency controlled sputtering, pulsed laser sputtering (PLD), atomic layer deposition (ALD), plasma chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD). Next, the electrically insulating material is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, but a dry etching process may also be selected, to form a pattern of the support layer 14.

[0087] S14 , forming a first electrode 11 on the support layer 14 .

[0088] In some examples, step S14 may include first depositing a metal film on the entire surface, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or the like. Next, the metal film is subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably by wet etching, but dry etching may also be employed, to form a pattern of the first electrode 11.

[0089] S15 , forming a piezoelectric layer 12 on the first electrode 11 .

[0090] In some examples, step S15 may include first performing oriented growth of the piezoelectric material, preferably by radio frequency magnetron sputtering. For AlN or Sc-doped AlN piezoelectric materials, the target material is selected as Al target or Al target + Sc target. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, a C-axis oriented AlN piezoelectric film or a Sc-doped AlN piezoelectric film is formed. The preferred growth orientation is (001), and it can also be (100) and (111) orientations. The film deposition method can also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. The piezoelectric layer 12 is deposited on the entire surface without performing photolithography and etching processes.

[0091] S16 , forming a second sacrificial layer 62 on the piezoelectric layer 12 and located in the peripheral region Q2 .

[0092] In some examples, step S16 may include first depositing a second sacrificial layer 62, preferably plasma-enhanced chemical vapor deposition (PECVD), but also low-pressure chemical vapor deposition (LPCVD), radio frequency magnetron sputtering, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), thermal evaporation, and electron beam evaporation. The second sacrificial layer 62 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, but a dry etching process may also be selected to form a pattern of the second sacrificial layer 62.

[0093] S17 , preparing a second electrode 13 on the piezoelectric layer 12 and the second sacrificial layer 62 .

[0094] In some examples, step S17 may include first depositing a metal film, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or the like. Next, the metal film is subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably by wet etching, but dry etching may also be employed, to form a pattern for the second electrode 13.

[0095] S18 , forming a mass load layer 16 on the second electrode 13 .

[0096] In some examples, step S18 may include first depositing a mass load layer 16 thin film, wherein the deposition method is preferably plasma enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD), radio frequency magnetron sputtering, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), thermal evaporation, electron beam evaporation, and organic material liquid coating (spin coating, spraying, inkjet printing, transfer, etc., followed by heating and curing). Next, the mass load layer 16 undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, and a dry etching process can also be selected to form a pattern of the mass load layer 16.

[0097] S19 , forming a release hole of the first sacrificial layer 61 .

[0098] In some examples, step S19 may include performing a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. A dry etching process is preferred, but a wet etching process may also be selected. A multi-step dry etching process is used to first etch the piezoelectric layer 12. When etching reaches the first electrode 11, the etching gas is replaced to continue etching the first electrode 11. When etching reaches the support layer 14, the etching gas is replaced again to continue etching the support layer 14 until etching reaches the first sacrificial layer 61.

[0099] S110 , etching and releasing the first sacrificial layer 61 of the air gap sound reflection layer structure.

[0100] In some examples, a dry etching process is preferably used in step S110 to completely etch away the boron- and phosphorus-doped silicon dioxide or boron-doped loose silicon dioxide or phosphorus-doped loose silicon dioxide film between the substrate 10 and the support layer 14 .

[0101] S111 , the second sacrificial layer 62 is released between the second electrode 13 and the piezoelectric layer 12 to form a second air gap 42 .

[0102] In some examples, a dry etching process is preferably used in step S111 to completely etch away the boron- and phosphorus-doped silicon dioxide or boron-doped loose silicon dioxide or phosphorus-doped loose silicon dioxide film between the first electrode 11 and the piezoelectric layer 12 .

[0103] S112 , forming a first air gap 41 penetrating the piezoelectric layer 12 and the first electrode 11 in the peripheral region Q2 .

[0104] In some examples, step S112 may include first performing a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. A dry etching process is preferably used, and a wet etching process may also be used to etch the piezoelectric layer 12. The etching depth can be flexibly adjusted with the length of the etching time (partial etching of the piezoelectric layer 12, complete etching of the piezoelectric layer 12 to the first electrode 11, partial etching of the first electrode 11, and complete etching of the first electrode 11 to the support layer 14) to form a shallow longitudinal air gap structure or a deep longitudinal air gap structure, that is, to form a first air gap 41.

[0105] Second example: FIG10 is a schematic diagram of a bulk acoustic wave resonator of the second example of an embodiment of the present disclosure; as shown in FIG10 , the bulk acoustic wave resonator is divided into a working area Q1 and a peripheral area Q2 surrounding the working area Q1. The bulk acoustic wave resonator includes a substrate 10, and at least one layer of an acoustic reflector 15 structure, a first electrode 11, a piezoelectric layer 12, and a second electrode 13 sequentially arranged on the substrate 10. The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the substrate 10 at least partially overlap. The reflector 15 structure includes a first substructure and a second substructure sequentially arranged in a direction away from the substrate 10, and the acoustic impedance of the material of the first substructure is greater than the acoustic impedance of the material of the second substructure. For ease of description and understanding, the first substructure is hereinafter referred to as the high acoustic impedance layer 151, and the second substructure is referred to as the low acoustic impedance layer 152. In the working area Q1 , the first electrode 11 and the second electrode 13 are respectively attached to the upper and lower surfaces of the piezoelectric layer 12 . In the peripheral area Q2 , a first air gap 41 is provided that penetrates at least part of the thickness of the piezoelectric layer 12 in a direction perpendicular to the base substrate 10 .

[0106] In some examples, Figure 11 is a schematic diagram of another bulk acoustic wave resonator of the second example of the embodiment of the present disclosure; Figure 12 is a schematic diagram of yet another bulk acoustic wave resonator of the second example of the embodiment of the present disclosure; as shown in Figures 10-12, the first air gap 41 can completely penetrate the piezoelectric layer 12, or only penetrate part of the thickness of the piezoelectric layer 12, or the first air gap 41 can also penetrate the piezoelectric layer 12 and the first electrode 11. Of course, the first air gap 41 can also penetrate at least part of the thickness of the piezoelectric layer 12, the first electrode 11 and the reflector 15 structure, for example, penetrating the piezoelectric layer 12, the first electrode 11 and the low acoustic impedance structure closest to the first electrode 11.

[0107] Referring to Figure 10, the input RF signal is converted into an acoustic wave signal through the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, which propagates longitudinally in the piezoelectric layer 12. When it reaches the interface between the first electrode 11 and the piezoelectric layer 12, it is converted into an RF signal again through the piezoelectric effect and then transmitted out. The reflector 15 below the resonator and the air layer above it act as acoustic reflectors, and their function is to confine the acoustic signal within the resonator structure rather than dissipate it, thereby reducing the loss of the resonator. At the same time, a first air gap 41 is formed in the peripheral area Q2, that is, a longitudinal air wall structure is formed, so that the acoustic waves propagating laterally near the piezoelectric layer 12 and the first electrode 11 are fully reflected at the air wall structure and return to the piezoelectric resonator instead of propagating outward and dissipating, thereby reducing the loss of the device.

[0108] In some examples, with continued reference to Figures 10-12, the BAW resonator includes not only the aforementioned structure but also a second air gap 42 defined in the peripheral region Q2 by the piezoelectric layer 12 and the second electrode 13. Specifically, the second electrode 13 includes a main body portion and an edge portion connected to the main body portion, wherein the main body portion is located in the working region Q1 and the edge portion is located in the peripheral region Q2. The main body portion contacts the piezoelectric layer 12, and a certain gap is formed between the edge portion and the piezoelectric layer 12, forming the second air gap 42. The second air gap 42 allows acoustic waves propagating laterally within the piezoelectric layer 12 to be fully reflected at the wall structure and return to the piezoelectric resonator rather than propagating outward and dissipating, thereby reducing device losses.

[0109] In some examples, a mass load layer 16 may be further provided on the side of the second electrode 13 facing away from the base substrate 10. On the one hand, the film layer can isolate water vapor and oxygen, act as a package, and prevent the performance of the piezoelectric resonator from deteriorating over time. On the other hand, when the frequency of the piezoelectric resonator shifts, the frequency of the piezoelectric resonator can be adjusted and corrected to an ideal value by performing local plasma etching on the mass load layer 16.

[0110] The mass-loading layer 16 is preferably made of inorganic materials such as SiNx, Al2O3, SiO2, AlN, BN, and other materials that can isolate water vapor and oxygen. Alternatively, various metal materials (such as Mo, Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, Se, or alloys of various metals or stacks of various metal layers) or organic compounds such as polyimide and epoxy resin may be selected. The mass-loading layer 16 may be a single layer of a single material or a stack of multiple materials.

[0111] In some examples, the base substrate 10 is preferably Si, and materials such as glass, sapphire, SiC, GaAs, GaN, InP, BN, and ZnO may also be selected. The thickness of the base substrate 10 ranges from 0.1 um to 10 mm.

[0112] In some examples, the first electrode 11 is preferably made of molybdenum. Alternatively, materials such as Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, or Se may be used. Alternatively, an alloy of the above metals or a stack of metal layers may be used. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0113] In some examples, the piezoelectric layer 12 is preferably AlN, followed by Sc-doped AlN, and may also be BN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. It can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0114] In some examples, the second electrode 13 is preferably made of molybdenum. Other materials include Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, and Se. An alloy of the above metals or a stack of metal layers may also be used. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0115] In some examples, the reflector 15 structure is composed of alternating high-acoustic impedance layers 151 and low-acoustic impedance layers 152. The acoustic impedance of a material is equal to the speed of sound waves propagating through it multiplied by its density. Theoretically, when the thickness of the high-acoustic impedance layer 151 is equal to one-quarter of the wavelength of sound waves at the resonant frequency of the bulk acoustic wave resonator propagating through the high-acoustic impedance layer 151, and the thickness of the low-acoustic impedance layer 152 is equal to one-quarter of the wavelength of sound waves at the resonant frequency of the bulk acoustic wave resonator propagating through the low-acoustic impedance layer 152, the alternating arrangement of high and low-acoustic impedance layers 152 (high / low / high / low, etc., or low / high / low / high, etc.) creates an acoustic reflector 15, which reflects sound signals leaking from above. The high-acoustic impedance layers 151 and low-acoustic impedance layers 152 form a reflector 15 structure. Generally, three to four sets are required to achieve a good acoustic reflection effect. Of course, the more sets, the better, but the cost will increase. There is no limit on the number of groups, and the reflector 15 structure can be selected from 1 to 100 layers. There is no limit on whether it is equal to one-quarter of the wavelength; any thickness is acceptable. Materials for the high acoustic impedance layer 151 can include W, Ir, Pt, Ru, Au, Mo, Ta, Ti, Cu, Ni, Zn, Al, Al2O3, Ag, etc. Commonly used low acoustic impedance materials can include SiO2, Si3N4, Mg, rubber, nylon, polyimide, polyethylene, polystyrene, Teflon, etc. Depending on the resonant frequency and the different sound velocities of different materials, the thickness of a single high acoustic impedance layer 151 and a single low acoustic impedance layer 152 can range from 1 nm to 10 μm.

[0116] In this example, a method for preparing a BAW resonator is provided, taking the BAW resonator shown in FIG10 as an example. FIG13 is a flow chart of preparing the BAW resonator shown in FIG10 . As shown in FIG13 , the method specifically includes the following steps:

[0117] S21 , providing a base substrate 10 .

[0118] In this step, the base substrate 10 may be cleaned and then dried by an air knife.

[0119] S22 , forming a reflector 15 structure on the base substrate 10 .

[0120] In some examples, step S22 may include: (a) first depositing a thin film material for the high acoustic impedance layer 151, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, or electron beam evaporation. The high acoustic impedance layer 151 is then subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably by wet etching, but dry etching is also acceptable. This forms a pattern for the high acoustic impedance layer 151; and (b) then depositing a thin film material for the low acoustic impedance layer 152, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, or electron beam evaporation. The low acoustic impedance layer 152 is then subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably by wet etching, but dry etching is also acceptable. Form a pattern of the low acoustic impedance layer 152; then repeat steps (a) and (b) until an acoustic reflector 15 structure with the number of layers meeting the design requirements is obtained

[0121] S23 , forming a first electrode 11 on the reflector 15 structure.

[0122] In some examples, step S23 may include first depositing a metal thin film on the entire surface, preferably using DC magnetron sputtering (RF magnetron sputtering is also acceptable), but alternative methods include pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, and electron beam evaporation. Next, the metal thin film is subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably using a wet etching process, but also a dry etching process, to form a pattern of the first electrode 11.

[0123] S24 , forming a piezoelectric layer 12 on the first electrode 11 .

[0124] In some examples, step S24 may include first performing oriented growth of the piezoelectric material, preferably by radio frequency magnetron sputtering. For AlN or Sc-doped AlN piezoelectric materials, the target material is selected as Al target or Al target + Sc target. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, a C-axis oriented AlN piezoelectric film or a Sc-doped AlN piezoelectric film is formed. The preferred growth orientation is (001), and it can also be (100) and (111) orientations. The film deposition method can also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. The piezoelectric layer 12 is deposited on the entire surface without performing photolithography and etching processes.

[0125] S25 , forming a second sacrificial layer 62 on the piezoelectric layer 12 and located in the peripheral region Q2 .

[0126] In some examples, step S25 may include first depositing a second sacrificial layer 62, preferably plasma-enhanced chemical vapor deposition (PECVD), but also low-pressure chemical vapor deposition (LPCVD), radio frequency magnetron sputtering, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), thermal evaporation, and electron beam evaporation. The second sacrificial layer 62 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, but a dry etching process may also be selected to form a pattern of the second sacrificial layer 62.

[0127] S26 , preparing a second electrode 13 on the piezoelectric layer 12 and the second sacrificial layer 62 .

[0128] In some examples, step S26 may include first depositing a metal film, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or the like. Next, the metal film is subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably by wet etching, but dry etching may also be employed, to form a pattern for the second electrode 13.

[0129] S27 , forming a mass load layer 16 on the second electrode 13 .

[0130] In some examples, step S27 may include first depositing a mass load layer 16 thin film, wherein the deposition method is preferably plasma enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD), radio frequency magnetron sputtering, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), thermal evaporation, electron beam evaporation, and organic material liquid coating (spin coating, spraying, inkjet printing, transfer, etc., followed by heating and curing). Next, the mass load layer 16 undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, and a dry etching process can also be selected to form a pattern of the mass load layer 16.

[0131] S28 , the second sacrificial layer 62 is released between the second electrode 13 and the piezoelectric layer 12 , forming a second air gap 42 .

[0132] In some examples, a dry etching process is preferably used in step S28 to completely etch away the boron- and phosphorus-doped silicon dioxide or boron-doped loose silicon dioxide or phosphorus-doped loose silicon dioxide film between the first electrode 11 and the piezoelectric layer 12 .

[0133] S29. Form a first air gap 41 penetrating the piezoelectric layer 12 in the peripheral region Q2.

[0134] In some examples, step S29 may include first performing a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. A dry etching process is preferably used, but a wet etching process may also be used to etch the piezoelectric layer 12. The etching depth can be flexibly adjusted with the etching time (partial etching of the piezoelectric layer 12, complete etching of the piezoelectric layer 12 to the first electrode 11), thereby forming the first air gap 41.

[0135] For the preparation method of the bulk acoustic wave resonator shown in Figure 11, only the structure of the first gap in the above-mentioned bulk acoustic wave resonator is different. The formation of the first air gap 41 is completed after the second sacrificial layer 62 is released, and the first air gap 41 penetrates the piezoelectric layer 12 and the first electrode 11. This step can specifically include performing a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. A dry etching process is preferred, and a wet etching process can also be selected to etch the piezoelectric layer 12. The etching depth can be flexibly adjusted with the length of the etching time (partial etching of the piezoelectric layer 12, complete etching of the piezoelectric layer 12 to the first electrode 11, partial etching of the first electrode 11, complete etching of the first electrode 11 to the low acoustic impedance layer 152), forming a shallow longitudinal air gap structure or a deep longitudinal air gap structure, that is, forming the first air gap 41.

[0136] The method for fabricating the BAW resonator shown in FIG12 differs only in the structure of the first air gap in the BAW resonator described above. The first air gap 41 is formed after the second sacrificial layer 62 is released, and the first air gap 41 penetrates the piezoelectric layer 12, the first electrode 11, and the low acoustic impedance layer 152 closest to the first electrode 11. The first air gap 41 is formed after the second sacrificial layer 62 is released, and the first air gap 41 penetrates the piezoelectric layer 12 and the low acoustic impedance layer 152 closest to the first electrode 11. This step may specifically include a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. A dry etching process is preferred, but a wet etching process can also be selected to etch the piezoelectric layer 12. The etching depth can be flexibly adjusted with the length of the etching time (partial etching of the piezoelectric layer 12, complete etching of the piezoelectric layer 12 to the first electrode 11, partial etching of the first electrode 11, complete etching of the first electrode 11 to the low acoustic impedance layer 152, partial etching of the low acoustic impedance layer 152, complete etching of the low acoustic impedance layer 152 to the high acoustic impedance layer 151) to form a shallow longitudinal air gap structure or a deep longitudinal air gap structure, that is, to form a first air gap 41.

[0137] Third example: FIG14 is a schematic diagram of a BAW resonator of the third example of an embodiment of the present disclosure; as shown in FIG14 , the BAW resonator is divided into a working area Q1 and a peripheral area Q2 surrounding the working area Q1, and the BAW resonator includes a substrate 10, and a first electrode 11, a piezoelectric layer 12, and a second electrode 13 sequentially arranged on the substrate 10. The substrate 10 includes a first surface (upper surface) and a second surface (lower surface) arranged opposite to each other along its thickness direction, and the first cavity 101 includes a first opening formed on the first surface and a second opening formed on the second surface. The first electrode 11 is arranged on the first surface, and the orthographic projection of the first electrode 11 on the plane where the second surface is located covers the orthographic projection of the first opening on the plane where the second surface is located. The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the substrate 10 at least partially overlap. In the working area Q1 , the first electrode 11 and the second electrode 13 are respectively attached to the upper and lower surfaces of the piezoelectric layer 12 . In the peripheral area Q2 , a first air gap 41 is provided that penetrates at least part of the thickness of the piezoelectric layer 12 in a direction perpendicular to the base substrate 10 .

[0138] In some examples, the first air gap 41 may completely penetrate the piezoelectric layer 12 or may only penetrate a portion of the thickness of the piezoelectric layer 12 . In this example, the first air gap 41 penetrating the piezoelectric layer 12 is taken as an example.

[0139] Referring to Figure 14, the input radio frequency signal is converted into an acoustic wave signal through the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, and propagates longitudinally in the piezoelectric layer 12. When it reaches the interface between the first electrode 11 and the piezoelectric layer 12, it is converted into an radio frequency signal through the piezoelectric effect and then transmitted. The first cavity 101 (air cavity) below the resonator and the air layer above it act as acoustic reflectors, whose function is to confine the acoustic signal to the resonator structure instead of dissipating it, thereby reducing the loss of the resonator. At the same time, the piezoelectric layer 12 is interrupted in the peripheral area Q2 to form a first air gap 41, that is, a longitudinal air wall structure is formed, so that the acoustic waves propagating laterally near the piezoelectric layer 12 are fully reflected at the air wall structure and return to the piezoelectric resonator instead of propagating outward and dissipating, thereby reducing the loss of the device.

[0140] In some examples, with continued reference to FIG. 14 , the BAW resonator includes not only the aforementioned structure but also a second air gap 42 defined in the peripheral region Q2 by the piezoelectric layer 12 and the second electrode 13. Specifically, the second electrode 13 includes a main body portion and an edge portion connected to the main body portion, wherein the main body portion is located in the working region Q1 and the edge portion is located in the peripheral region Q2. The main body portion contacts the piezoelectric layer 12, and a certain gap is formed between the edge portion and the piezoelectric layer 12, forming the second air gap 42. The second air gap 42 allows acoustic waves propagating laterally within the piezoelectric layer 12 to be fully reflected at the wall structure and return to the piezoelectric resonator rather than propagating outward and dissipating, thereby reducing device losses.

[0141] In some examples, a mass load layer 16 may be further provided on the side of the second electrode 13 facing away from the base substrate 10. On the one hand, the film layer can isolate water vapor and oxygen, act as a package, and prevent the performance of the piezoelectric resonator from deteriorating over time. On the other hand, when the frequency of the piezoelectric resonator shifts, the frequency of the piezoelectric resonator can be adjusted and corrected to an ideal value by performing local plasma etching on the mass load layer 16.

[0142] The mass-loading layer 16 is preferably made of inorganic materials such as SiNx, Al2O3, SiO2, AlN, BN, and other materials that can isolate water vapor and oxygen. Alternatively, various metal materials (such as Mo, Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, Se, or alloys of various metals or stacks of various metal layers) or organic compounds such as polyimide and epoxy resin may be selected. The mass-loading layer 16 may be a single layer of a single material or a stack of multiple materials.

[0143] In some examples, the base substrate 10 is preferably Si, and may also be made of glass, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, etc. The thickness of the base substrate 10 ranges from 0.1 um to 10 mm.

[0144] In some examples, the first electrode 11 is preferably made of molybdenum. Alternatively, materials such as Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, or Se may be used. Alternatively, an alloy of the above metals or a stack of metal layers may be used. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0145] In some examples, the piezoelectric layer 12 is preferably AlN, followed by Sc-doped AlN, and may also be BN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. It can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0146] In some examples, the second electrode 13 is preferably made of molybdenum. Other materials include Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, and Se. An alloy of the above metals or a stack of metal layers may also be used. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0147] In an embodiment of the present disclosure, a method for preparing the BAW resonator is provided. FIG15 is a flow chart of preparing the BAW resonator shown in FIG14 . As shown in FIG14 , the preparation method specifically includes the following steps:

[0148] S31 , providing a base substrate 10 .

[0149] In this step, the base substrate 10 may be cleaned and then dried by an air knife.

[0150] S32 , forming a first electrode 11 on the base substrate 10 .

[0151] In some examples, step S32 may include first depositing a metal film on the entire surface, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), but alternative methods include pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, and electron beam evaporation. Next, the metal film is subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably by wet etching, but dry etching is also acceptable, to form a pattern for the first electrode 11.

[0152] S33 , forming a piezoelectric layer 12 on the first electrode 11 .

[0153] In some examples, step S33 may include first performing oriented growth of the piezoelectric material, preferably by radio frequency magnetron sputtering. For AlN or Sc-doped AlN piezoelectric materials, the target material is selected as Al target or Al target + Sc target. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, a C-axis oriented AlN piezoelectric film or a Sc-doped AlN piezoelectric film is formed. The preferred growth orientation is (001), and may also be (100) and (111) orientations. The film deposition method may also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. The piezoelectric layer 12 is deposited on the entire surface without performing photolithography and etching processes.

[0154] S34 , forming a second sacrificial layer 62 on the piezoelectric layer 12 and located in the peripheral region Q2 .

[0155] In some examples, step S34 may include first depositing a second sacrificial layer 62, preferably plasma-enhanced chemical vapor deposition (PECVD), but also low-pressure chemical vapor deposition (LPCVD), radio frequency magnetron sputtering, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), thermal evaporation, and electron beam evaporation. The second sacrificial layer 62 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, but a dry etching process may also be selected to form a pattern of the second sacrificial layer 62.

[0156] S35 , preparing a second electrode 13 on the piezoelectric layer 12 and the second sacrificial layer 62 .

[0157] In some examples, step S35 may include first depositing a metal film, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or the like. Next, the metal film is subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably by wet etching, but dry etching may also be employed, to form a pattern for the second electrode 13.

[0158] S36 , forming a mass load layer 16 on the second electrode 13 .

[0159] In some examples, step S36 may include first depositing a mass load layer 16 thin film, where the deposition method is preferably plasma enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD), radio frequency magnetron sputtering, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), thermal evaporation, electron beam evaporation, and organic material liquid coating (spin coating, spraying, inkjet printing, transfer, etc., followed by heating and curing). Next, the mass load layer 16 undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, and a dry etching process may also be selected to form a pattern of the mass load layer 16.

[0160] S37 , the second sacrificial layer 62 is released between the second electrode 13 and the piezoelectric layer 12 , forming a second air gap 42 .

[0161] In some examples, a dry etching process is preferably used in step S37 to completely etch away the boron- and phosphorus-doped silicon dioxide or boron-doped loose silicon dioxide or phosphorus-doped loose silicon dioxide film between the first electrode 11 and the piezoelectric layer 12 .

[0162] S38. Form a first air gap 41 penetrating the piezoelectric layer 12 in the peripheral region Q2.

[0163] In some examples, step S38 may include first performing a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. A dry etching process is preferably used, but a wet etching process may also be used to etch the piezoelectric layer 12. The etching depth can be flexibly adjusted with the etching time (partial etching of the piezoelectric layer 12, complete etching of the piezoelectric layer 12 to the first electrode 11), thereby forming the first air gap 41.

[0164] S39 , turning over the base substrate 10 after the above steps to form a first cavity 101 .

[0165] In some examples, step S39 may include first depositing a mask material on the substrate 10 (optional mask materials include photoresist, inorganic mask or metal mask). Next, a photolithography process is performed, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, which can be dry etching or wet etching, preferably wet etching, to form a mask. Then, the substrate 10 is etched, which can be wet etching or dry etching, preferably wet etching, and the etching stops at the first electrode 11 to form an air sound reflection layer, that is, to form the first cavity 101. When the substrate 10 is a Si substrate, the etching solution of the Si substrate 10 is: (1) an isotropic etching solution, the composition ratio of which is hydrofluoric acid: nitric acid: water (or acetic acid) = 3:2:5, and the etching rate is 10 to 50 um / min. (2) Anisotropic etching solutions can be selected from a mixture of ethylenediamine, o-diphenol, and pyrazine, an aqueous solution of tetramethylhydroxylamine, an aqueous solution of sodium hydroxide, or an aqueous solution of potassium hydroxide. The etching rate is 0.5 to 2 μm / minute. When the substrate 10 is a glass substrate, the etching solution for the glass substrate 10 is a mixture of 3% to 7% hydrofluoric acid, 20% to 30% ammonium fluoride, and deionized water. Finally, the mask material is removed.

[0166] Fourth example: FIG16 is a schematic diagram of a bulk acoustic wave resonator of the fourth example of the embodiment of the present disclosure; as shown in FIG16 , the bulk acoustic wave resonator is divided into a working area Q1 and a peripheral area Q2 surrounding the working area Q1. The bulk acoustic wave resonator includes a substrate 10, and a support layer 14, a first electrode 11, a piezoelectric layer 12, and a second electrode 13 sequentially arranged on the substrate 10. The substrate 10 includes a first surface (upper surface) and a second surface (lower surface) arranged opposite to each other along its thickness direction, and the first cavity 101 includes a first opening formed on the first surface and a second opening formed on the second surface. The support layer 14 is arranged on the first surface, and the orthographic projection of the support layer 14 on the plane where the second surface is located covers the orthographic projection of the first opening on the plane where the second surface is located. The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the substrate 10 at least partially overlap. In the working area Q1 , the first electrode 11 and the second electrode 13 are respectively attached to the upper and lower surfaces of the piezoelectric layer 12 . In the peripheral area Q2 , a first air gap 41 is provided that penetrates at least part of the thickness of the piezoelectric layer 12 in a direction perpendicular to the base substrate 10 .

[0167] In some examples, FIG17 is a schematic diagram of another BAW resonator according to a fourth example of an embodiment of the present disclosure. As shown in FIG16 and FIG17 , the first air gap 41 may completely penetrate the piezoelectric layer 12 or only partially penetrate the thickness of the piezoelectric layer 12. Of course, the first air gap 41 may also penetrate the piezoelectric layer 12 and the first electrode 11. In this example, only the case where the first air gap 41 penetrates the piezoelectric layer 12 is used as an example.

[0168] Referring to Figure 16, the input radio frequency signal is converted into an acoustic wave signal through the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, and propagates longitudinally in the piezoelectric layer 12. When it reaches the interface between the first electrode 11 and the piezoelectric layer 12, it is converted into an radio frequency signal through the piezoelectric effect and then transmitted. The first cavity 101 (air cavity) below the resonator and the air layer above it act as acoustic reflectors, whose function is to confine the acoustic signal to the resonator structure instead of dissipating it, thereby reducing the loss of the resonator. At the same time, the piezoelectric layer 12 is interrupted in the peripheral area Q2 to form a first air gap 41, that is, a longitudinal air wall structure is formed, so that the acoustic waves propagating laterally near the piezoelectric layer 12 are fully reflected at the air wall structure and return to the piezoelectric resonator instead of propagating outward and dissipating, thereby reducing the loss of the device.

[0169] In some examples, with continued reference to Figures 16 and 17, the BAW resonator includes not only the aforementioned structure, but also a second air gap 42 defined in the peripheral region Q2 by the piezoelectric layer 12 and the second electrode 13. Specifically, the second electrode 13 includes a main body portion and an edge portion connected to the main body portion, wherein the main body portion is located in the working region Q1, and the edge portion is located in the peripheral region Q2. The main body portion contacts the piezoelectric layer 12, and a certain gap is formed between the edge portion and the piezoelectric layer 12, forming the second air gap 42. The second air gap 42 allows acoustic waves propagating laterally within the piezoelectric layer 12 to be fully reflected at the wall structure and return to the piezoelectric resonator instead of propagating outward and being dissipated, thereby reducing device losses.

[0170] In some examples, a mass load layer 16 may be further provided on the side of the second electrode 13 facing away from the base substrate 10. On the one hand, the film layer can isolate water vapor and oxygen, act as a package, and prevent the performance of the piezoelectric resonator from deteriorating over time. On the other hand, when the frequency of the piezoelectric resonator shifts, the frequency of the piezoelectric resonator can be adjusted and corrected to an ideal value by performing local plasma etching on the mass load layer 16.

[0171] The mass-loading layer 16 is preferably made of inorganic materials such as SiNx, Al2O3, SiO2, AlN, BN, and other materials that can isolate water vapor and oxygen. Alternatively, various metal materials (such as Mo, Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, Se, or alloys of various metals or stacks of various metal layers) or organic compounds such as polyimide and epoxy resin may be selected. The mass-loading layer 16 may be a single layer of a single material or a stack of multiple materials.

[0172] In some examples, the base substrate 10 is preferably Si, and materials such as glass, sapphire, SiC, GaAs, GaN, InP, BN, and ZnO may also be selected. The thickness of the base substrate 10 ranges from 0.1 um to 10 mm.

[0173] In some examples, the first electrode 11 is preferably made of molybdenum. Alternatively, materials such as Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, or Se may be used. Alternatively, an alloy of the above metals or a stack of metal layers may be used. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0174] In some examples, the piezoelectric layer 12 is preferably AlN, followed by Sc-doped AlN, and may also be BN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. It can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0175] In some examples, the second electrode 13 is preferably made of molybdenum. Other materials include Al, Cu, Co, Ag, Ti, Pt, Ru, W, Au, Cr, Fe, Zn, Mg, Ni, Sn, Pb, Ce, Bi, Nb, Pd, Rh, Tl, Ir, U, Ta, Te, Th, V, Ba, Mn, Cd, Ge, Zr, and Se. An alloy of the above metals or a stack of metal layers may also be used. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0176] In some examples, the support layer 14 is preferably made of electrically insulating Si3N4, but may also be made of SiO2, Al2O3, AlN, BN, etc. It may be a single material or a stack of the above materials. The thickness of the support layer 14 ranges from 1 nm to 10 μm.

[0177] In an embodiment of the present disclosure, a method for preparing the BAW resonator is provided. FIG18 is a flow chart of preparing the BAW resonator shown in FIG16 . As shown in FIG18 , the method specifically includes the following steps:

[0178] S41 , providing a base substrate 10 .

[0179] In this step, the base substrate 10 may be cleaned and then dried by an air knife.

[0180] S42 , forming a support layer 14 on the base substrate 10 .

[0181] In some examples, step S42 may include first depositing the entire surface of the electrically insulating material, and the deposition method may be RF sputtering, pulsed laser sputtering (PLD), atomic layer deposition (ALD), plasma chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD). Next, the electrically insulating material is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, and a dry etching process may also be selected to form a pattern of the support layer 14.

[0182] S43 , forming a first electrode 11 on the support layer 14 .

[0183] In some examples, step S43 may include first depositing a metal thin film on the entire surface, preferably using DC magnetron sputtering (RF magnetron sputtering is also acceptable), but alternative methods include pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, and electron beam evaporation. Next, the metal thin film is subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably using a wet etching process, but also a dry etching process, to form a pattern of the first electrode 11.

[0184] S44 , forming a piezoelectric layer 12 on the first electrode 11 .

[0185] In some examples, step S44 may include first performing oriented growth of the piezoelectric material, preferably by radio frequency magnetron sputtering. For AlN or Sc-doped AlN piezoelectric materials, the target material is selected as Al target or Al target + Sc target. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, a C-axis oriented AlN piezoelectric film or a Sc-doped AlN piezoelectric film is formed. The preferred growth orientation is (001), and may also be (100) and (111) orientations. The film deposition method may also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. The piezoelectric layer 12 is deposited on the entire surface without performing photolithography and etching processes.

[0186] S45 , forming a second sacrificial layer 62 on the piezoelectric layer 12 and located in the peripheral region Q2 .

[0187] In some examples, step S45 may include first depositing a second sacrificial layer 62, preferably plasma-enhanced chemical vapor deposition (PECVD), but also low-pressure chemical vapor deposition (LPCVD), radio frequency magnetron sputtering, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal-organic chemical vapor deposition (MOCVD), thermal evaporation, and electron beam evaporation. The second sacrificial layer 62 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, but a dry etching process may also be selected to form a pattern of the second sacrificial layer 62.

[0188] S46 , preparing a second electrode 13 on the piezoelectric layer 12 and the second sacrificial layer 62 .

[0189] In some examples, step S46 may include first depositing a metal film, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or the like. Next, the metal film is subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably by wet etching, but dry etching may also be employed, to form a pattern for the second electrode 13.

[0190] S47 , forming a mass load layer 16 on the second electrode 13 .

[0191] In some examples, step S47 may include first depositing a mass load layer 16 thin film, wherein the deposition method is preferably plasma enhanced chemical vapor deposition (PECVD), and low pressure chemical vapor deposition (LPCVD), radio frequency magnetron sputtering, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), thermal evaporation, electron beam evaporation, and organic material liquid coating (spin coating, spraying, inkjet printing, transfer, etc., followed by heating and curing). Next, the mass load layer 16 undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, and a dry etching process can also be selected to form a pattern of the mass load layer 16.

[0192] S48 , the second sacrificial layer 62 is released between the second electrode 13 and the piezoelectric layer 12 , forming a second air gap 42 .

[0193] In some examples, a dry etching process is preferably used in step S37 to completely etch away the boron- and phosphorus-doped silicon dioxide or boron-doped loose silicon dioxide or phosphorus-doped loose silicon dioxide film between the first electrode 11 and the piezoelectric layer 12 .

[0194] S49 , forming a first air gap 41 penetrating the piezoelectric layer 12 in the peripheral region Q2 .

[0195] In some examples, step S49 may include first performing a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. A dry etching process is preferably used, but a wet etching process may also be used to etch the piezoelectric layer 12. The etching depth can be flexibly adjusted with the etching time (partial etching of the piezoelectric layer 12, complete etching of the piezoelectric layer 12 to the first electrode 11), thereby forming the first air gap 41.

[0196] S410 , turning over the base substrate 10 after the above steps to form a first cavity 101 .

[0197] In some examples, step S410 may include first depositing a mask material on the substrate 10 (optional mask materials include photoresist, inorganic mask or metal mask). Next, a photolithography process is performed, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, which can be dry etching or wet etching, preferably wet etching, to form a mask. Then, the substrate 10 is etched, which can be wet etching or dry etching, preferably wet etching, and the etching stops at the first electrode 11 to form an air sound reflection layer, that is, to form the first cavity 101. When the substrate 10 is a Si substrate, the etching solution of the Si substrate 10 is: (1) an isotropic etching solution, the composition ratio of which is hydrofluoric acid: nitric acid: water (or acetic acid) = 3:2:5, and the etching rate is 10 to 50 um / minute. (2) Anisotropic etching solutions can be selected from a mixture of ethylenediamine, o-diphenol, and pyrazine, an aqueous solution of tetramethylhydroxylamine, an aqueous solution of sodium hydroxide, or an aqueous solution of potassium hydroxide. The etching rate is 0.5 to 2 μm / minute. When the substrate 10 is a glass substrate, the etching solution for the glass substrate 10 is a mixture of 3% to 7% hydrofluoric acid, 20% to 30% ammonium fluoride, and deionized water. Finally, the mask material is removed.

[0198] For the preparation method of the bulk acoustic wave resonator shown in Figure 17, only the structure of the first gap in the above-mentioned bulk acoustic wave resonator is different. The formation of the first air gap 41 is completed after the second sacrificial layer 62 is released, and the first air gap 41 penetrates the piezoelectric layer 12 and the first electrode 11. This step can specifically include performing a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. A dry etching process is preferred, and a wet etching process can also be selected to etch the piezoelectric layer 12. The etching depth can be flexibly adjusted with the length of the etching time (partial etching of the piezoelectric layer 12, complete etching of the piezoelectric layer 12 to the first electrode 11, partial etching of the first electrode 11, complete etching of the first electrode 11 to the low acoustic impedance layer 152), forming a shallow longitudinal air gap structure or a deep longitudinal air gap structure, that is, forming the first air gap 41.

[0199] An embodiment of the present disclosure further provides an electronic device, which may include any of the above-mentioned bulk acoustic wave resonators.

[0200] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A bulk acoustic wave resonator, comprising: a substrate, a first electrode, a piezoelectric layer, and a second electrode; The first electrode is arranged on the substrate, the second electrode is arranged on a side of the first electrode facing away from the substrate, the piezoelectric layer is arranged between the first electrode and the second electrode, and the orthographic projections of any two of the first electrode, the piezoelectric layer and the second electrode on the substrate at least partially overlap; wherein, The BAW resonator is divided into a working area and a peripheral area surrounding the working area; the BAW resonator includes a first air gap located in the peripheral area, and the first air gap penetrates at least part of the thickness of the piezoelectric layer along a direction perpendicular to the substrate.

2. The bulk acoustic wave resonator according to claim 1, wherein The first air gap penetrates the piezoelectric layer in a direction perpendicular to the substrate.

3. The BAW resonator according to claim 1, wherein The first air gap penetrates the piezoelectric layer and the first electrode along a direction perpendicular to the substrate.

4. The BAW resonator according to claim 1, wherein The second electrode includes a main body located in the working area and an edge portion located in the peripheral area and connected to the main body. The main body contacts the piezoelectric layer, and a certain gap is formed between the edge portion and the piezoelectric layer to form a second air gap.

5. The BAW resonator according to claim 4, wherein The first air gap and the orthographic projection of the edge portion on the plane where the base substrate is located do not overlap.

6. The BAW resonator according to claim 4, wherein: The first air gap partially overlaps with an orthographic projection of the edge portion on the plane where the base substrate is located.

7. The BAW resonator according to claim 1, wherein The orthographic projection of the first air gap on the plane where the substrate is located is annular.

8. The BAW resonator according to claim 1, wherein The first air gap includes a plurality of spaced-apart sub-air gaps disposed around the working area.

9. The bulk acoustic wave resonator according to any one of claims 1 to 8, wherein: The base substrate has a first cavity extending through the base substrate along its thickness direction; the base substrate includes a first surface and a second surface arranged opposite to each other along its thickness direction; the first cavity includes a first opening and a second opening arranged opposite to each other; the first opening is located on the first surface, and the second opening is located on the second surface; the first electrode covers the first opening.

10. The bulk acoustic wave resonator according to any one of claims 1 to 8, wherein: The base substrate has a first groove portion; the base substrate includes a first surface and a second surface arranged opposite to each other along its thickness direction; the first groove portion includes a third opening, and the third opening is located on the first surface; the first electrode is located on the first surface; the outline of the orthographic projection of the third opening on the second surface is within the outline of the orthographic projection of the first electrode on the second surface.

11. The BAW resonator according to claim 10, wherein: A supporting layer is provided between the first surface of the base substrate and the first electrode.

12. The bulk acoustic wave resonator according to any one of claims 1 to 8, wherein: It also includes a supporting layer arranged between the base substrate and the first electrode; a certain space is defined between the supporting layer and the base substrate.

13. The bulk acoustic wave resonator according to any one of claims 1 to 8, wherein: It also includes at least one layer of reflector structure arranged between the first electrode and the base substrate; the reflector structure includes a first substructure layer and a second substructure layer arranged in sequence along a direction away from the base substrate, and the acoustic impedance of the material of the first substructure layer is greater than the acoustic impedance of the material of the second substructure layer.

14. The BAW resonator according to claim 13, wherein: The first air gap penetrates the piezoelectric layer, the first electrode, and the second substructure layer closest to the first electrode.

15. The bulk acoustic wave resonator according to any one of claims 1 to 8, wherein: The invention also includes a mass loading layer arranged on a side of the second electrode away from the substrate.

16. A method for preparing a bulk acoustic wave resonator, comprising: The step of sequentially forming a first electrode, a piezoelectric layer, and a second electrode on a base substrate, wherein the orthographic projections of any two of the first electrode, the piezoelectric layer, and the second electrode on the base substrate at least partially overlap; wherein the bulk acoustic wave resonator is divided into a working area and a peripheral area surrounding the working area; The preparation method further comprises: forming a first air gap in the peripheral area; The device penetrates at least a portion of the thickness of the piezoelectric layer in a direction perpendicular to the substrate.

17. The method for preparing a bulk acoustic wave resonator according to claim 16, wherein: The first air gap penetrates the piezoelectric layer in a direction perpendicular to the substrate.

18. The method for preparing a bulk acoustic wave resonator according to claim 16, wherein: The first air gap penetrates the piezoelectric layer and the first electrode along a direction perpendicular to the substrate.

19. The method for preparing a bulk acoustic wave resonator according to claim 16, wherein: The method further comprises: forming a second sacrificial layer in a peripheral area of ​​the piezoelectric layer after forming the piezoelectric layer; The second electrode is formed on the side of the second sacrificial layer and the piezoelectric layer facing away from the base substrate; after the second electrode is formed, the second sacrificial layer is etched away so that the second electrode includes a main body located in the working area, and an edge portion located in the peripheral area and connected to the main body, the main body is in contact with the piezoelectric layer, and the edge portion has a certain gap with the piezoelectric layer to form a second air gap.

20. The method for preparing a bulk acoustic wave resonator according to claim 16, wherein: The orthographic projection of the first air gap on the plane where the substrate is located is annular.

21. The method for preparing a bulk acoustic wave resonator according to claim 16, wherein: The first air gap includes a plurality of spaced-apart sub-air gaps disposed around the working area.

22. The method for preparing a bulk acoustic wave resonator according to any one of claims 16 to 21, wherein: The preparation method also includes: processing the base substrate to form a first cavity extending through the base substrate in a thickness direction; the base substrate includes a first surface and a second surface disposed opposite to each other in a thickness direction; the first cavity includes a first opening and a second opening disposed opposite to each other; the first opening is located on the first surface, and the second opening is located on the second surface; and the first electrode covers the first opening.

23. The method for preparing a bulk acoustic wave resonator according to any one of claims 16 to 21, wherein: The preparation method also includes: processing the base substrate to form a first groove portion; the base substrate includes a first surface and a second surface arranged opposite to each other along its thickness direction; the first groove portion includes a third opening, and the third opening is located on the first surface; the first electrode is located on the first surface; the outline of the positive projection of the third opening on the second surface is within the outline of the positive projection of the first electrode on the second surface.

24. The method for preparing a bulk acoustic wave resonator according to claim 23, wherein: Also includes: forming a first sacrificial layer in the first groove; forming a support layer on a side of the first groove portion facing away from the base substrate; The first electrode is formed on a side of the support layer away from the base substrate; A first through hole is formed through the first electrode and the support layer, and the first sacrificial layer is removed by etching through the first through hole.

25. The method for preparing a bulk acoustic wave resonator according to any one of claims 16 to 21, wherein: The preparation method further comprises: forming a first sacrificial layer on the base substrate; forming a supporting layer on a side of the first sacrificial layer away from the base substrate; and forming the first electrode on a side of the supporting layer away from the base substrate; A first through hole is formed through the first electrode and the support layer, and the first sacrificial layer is removed by etching through the first through hole.

26. The method for preparing a bulk acoustic wave resonator according to any one of claims 16 to 21, wherein: Before forming the first electrode, the method further includes: At least one reflector structure is formed on the base substrate; the reflector structure includes a first substructure layer and a second substructure layer formed in sequence along a direction away from the base substrate, and the acoustic impedance of the material of the first substructure layer is greater than the acoustic impedance of the material of the second substructure layer.

27. The method for preparing a bulk acoustic wave resonator according to claim 26, wherein: The first air gap penetrates the piezoelectric layer, the first electrode, and the second substructure layer closest to the first electrode.

28. The method for preparing a bulk acoustic wave resonator according to any one of claims 16 to 21, wherein: The preparation method further includes forming a mass loading layer on a side of the second electrode facing away from the substrate.

29. An electronic device comprising the bulk acoustic wave resonator according to any one of claims 1 to 15.

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