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

Abstract

The present disclosure provides a bulk acoustic wave resonator, a manufacturing method thereof, and electronic equipment, which belong to the field of communications technology. The bulk acoustic wave resonator of the present disclosure includes a first base substrate, a first electrode, a piezoelectric layer, and a second electrode, the first electrode being provided on the first base substrate, the second electrode being provided on a side of the first electrode away from the first base substrate, the piezoelectric layer being provided between the first electrode and the second electrode, any two of the first electrode, the piezoelectric layer, and the second electrode at least partially overlap when orthogonally projected on the first base substrate, and the sound velocity of the material of the piezoelectric layer is 18,000 m / s or more.

Description

[Technical Field]

[0001] The present disclosure belongs to the field of communications technology, and specifically relates to a bulk acoustic wave resonator, a manufacturing method thereof, and electronic equipment. [Background technology]

[0002] In the mobile communications field, the total allocated available frequency range is narrow, and there are many frequency bands used in mobile communications, with the spacing between adjacent frequency bands narrow (several MHz to several tens of MHz), and the bandwidth of a single frequency band narrow (several tens of MHz). Therefore, filters used in mobile phones must have the following performance characteristics: small in-band ripple, large out-of-band suppression, and good rectangularity. Conventional microstrip filters are large in volume, have insufficient out-of-band suppression, and have poor rectangularity, making them incompatible; cavity filters are large in volume, making them incompatible; dielectric filters have large in-band insertion loss and poor rectangularity, making them incompatible; and IPD filters have large in-band ripple and have poor rectangularity, making them incompatible.

[0003] A bulk acoustic wave resonator is the basic structural unit of a bulk acoustic wave filter. Conventional bulk acoustic wave resonators use a silicon wafer as the substrate material, on which a sandwich structure consisting of a first electrode, a piezoelectric material, and a second electrode is placed from bottom to top. The operating principle is that a radio frequency signal is input from the electrode at one end of the resonator, and then converted into a mechanically vibrating sound wave signal at the interface between the piezoelectric material and the metal electrode due to the inverse piezoelectric effect. This sound wave signal forms a standing wave with a certain resonating frequency in the sandwich structure of the first electrode, piezoelectric material, and second electrode, and the frequency of the radio frequency signal is equal to the resonant frequency of the resonator. The sound wave signal is then transmitted to the electrode at the other end of the resonator, and the sound wave signal is converted into a radio frequency signal at the interface between the metal electrode and the piezoelectric material due to the piezoelectric effect. The resonator has a certain resonant frequency. When the frequency of the radio frequency signal is equal to the resonant frequency of the resonator, the conversion efficiency of radio frequency signal → sound wave signal → radio frequency signal is high. When the frequency of the radio frequency signal is not equal to the resonant frequency of the resonator, the conversion efficiency of radio frequency signal → sound wave signal → radio frequency signal is low, and most of the radio frequency signal is not transmitted through the resonator. That is, the resonator functions as a filter and filters out the radio frequency signal. Summary of the Invention [Problem to be solved by the invention]

[0004] 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 manufacturing method thereof, and an electronic device. [Means for solving the problem]

[0005] An embodiment of the present disclosure provides a bulk acoustic wave resonator including a first base substrate, a first electrode, a piezoelectric layer, and a second electrode, wherein the first electrode is provided on the first base substrate, the second electrode is provided on a side of the first electrode away from the first base substrate, the piezoelectric layer is provided between the first electrode and the second electrode, any two of the first electrode, the piezoelectric layer, and the second electrode at least partially overlap in orthogonal projection on the first base substrate, and the sound velocity of the material of the piezoelectric layer is 18,000 m / s or more.

[0006] Here, the material of the piezoelectric layer includes any one of hBN, cBN, and wBN.

[0007] Here, the bulk acoustic wave resonator further includes a guide layer disposed between the first electrode and the piezoelectric layer, and the orthogonal projection of the guide layer on the first base substrate covers the orthogonal projection of the piezoelectric layer on the first base substrate.

[0008] Here, the material of the dielectric layer includes graphene.

[0009] Here, the piezoelectric element further includes a first connection electrode provided in the same layer as the second electrode, and the first connection electrode is electrically connected to the first electrode through a first connection via that penetrates the piezoelectric layer.

[0010] Here, the material of the first electrode includes one or more of Cu, Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au.

[0011] Here, the first base substrate has a first cavity penetrating through its thickness direction, the first base substrate includes a first surface and a second surface arranged opposite each other in the thickness direction, the first cavity includes a first opening and a second opening arranged opposite each other, the first opening is located on the first surface, the second opening is located on the second surface, and the first electrode covers the first opening.

[0012] Here, the first base substrate has a first groove portion, the first base substrate includes a first surface and a second surface arranged opposite each other in the thickness direction, the first groove portion includes a third opening located on the first surface, the first electrode is located on the first surface, and the contour of the orthogonal projection of the third opening on the second surface is within the contour of the orthogonal projection of the first electrode on the second surface.

[0013] Here, a separation layer is provided between the first surface of the first base substrate and the first electrode.

[0014] Here, the bulk acoustic wave resonator further includes at least one first through hole penetrating the first electrode and the isolation layer, the first through hole communicating with the first groove portion.

[0015] Here, the bulk acoustic wave resonator further includes at least one mirror structure layer provided between a first electrode and the first base substrate, the mirror structure including a first sub-structure layer and a second sub-structure layer sequentially provided in a direction away from the first base substrate, and the acoustic impedance of the material of the first sub-structure layer is greater than the acoustic impedance of the material of the second sub-structure layer.

[0016] Here, the bulk acoustic wave resonator further includes a packaging layer provided on a side of the second electrode away from the first base substrate, the packaging layer covering the first electrode, the piezoelectric layer, and the second electrode.

[0017] An embodiment of the present disclosure provides a method for manufacturing a bulk acoustic wave resonator, the method including sequentially forming a first electrode, a piezoelectric layer, and a second electrode on a first base substrate, wherein orthogonal projections of any two of the first electrode, the piezoelectric layer, and the second electrode on the first base substrate at least partially overlap, and the acoustic velocity of the material of the piezoelectric layer is 18,000 m / s or more.

[0018] Here, the material of the piezoelectric layer includes any one of hBN, cBN, and wBN.

[0019] Here, the step of forming the piezoelectric layer includes forming the piezoelectric layer using RF magnetron sputtering.

[0020] Here, the method further includes forming a dielectric layer before forming the first electrode and the piezoelectric layer.

[0021] Here, a first connection electrode is further formed at the same time as forming the second electrode, and the manufacturing method further includes forming a first connection via that penetrates the piezoelectric layer in its thickness direction, and the first connection electrode is connected to the first electrode through the first connection via.

[0022] Here, the manufacturing method further includes processing the first base substrate to include a first cavity penetrating the thickness direction of the first base substrate, the first base substrate including a first surface and a second surface arranged opposite to each other in the thickness direction, the first cavity including a first opening and a second opening arranged opposite to each other, the first opening being located on the first surface, the second opening being located on the second surface, and the first electrode covering the first opening.

[0023] Here, the manufacturing method further includes processing the first base substrate to have a first groove portion, the first base substrate including a first surface and a second surface arranged opposite each other in the thickness direction, the first groove portion including a third opening, the third opening being located on the first surface, the first electrode being located on the first surface, and the contour of the orthogonal projection of the third opening on the second surface being located within the contour of the orthogonal projection of the first electrode on the second surface.

[0024] Here, the method for manufacturing the bulk acoustic wave resonator includes the steps of: forming a filling structure in the first trench; forming an isolation layer on a side of the first groove portion away from the first base substrate, and forming the first electrode on the isolation layer on a side of the first groove portion away from the first base substrate; The method further includes forming a first through-hole that penetrates the first electrode and the isolation layer, and etching away the filling structure through the first through-hole.

[0025] Here, before forming the first electrode, The method further includes forming at least one layer of a mirror structure on the first base substrate, and forming the mirror structure including a first sub-structure layer and a second sub-structure layer formed sequentially in a direction away from the first base substrate, wherein the acoustic impedance of the material of the first sub-structure layer is greater than the acoustic impedance of the material of the second sub-structure layer.

[0026] Here, the method for manufacturing the bulk acoustic wave resonator further includes forming a packaging layer on a side of the second electrode away from the first base substrate, the packaging layer covering the first electrode, the piezoelectric layer and the second electrode.

[0027] An embodiment of the present disclosure provides an electronic device including any of the bulk acoustic wave resonators described above. [Brief explanation of the drawings]

[0028] [Figure 1] FIG. 1 is a schematic diagram of a back-etched bulk acoustic wave resonator. [Figure 2] FIG. 1 is a schematic diagram of a thin film bulk acoustic wave resonator. [Figure 3] 1 is a schematic diagram of a solid-state mounted bulk acoustic wave resonator. [Figure 4] 1 is a schematic diagram of a bulk acoustic wave resonator according to a first example of the present disclosure. [Figure 5] 5 is a flowchart for manufacturing the bulk acoustic wave resonator shown in FIG. [Figure 6] FIG. 2 is a schematic diagram of a bulk acoustic wave resonator according to a second example of the present disclosure. [Figure 7] 7 is a flowchart for manufacturing the bulk acoustic wave resonator shown in FIG. 6. [Figure 8] FIG. 10 is a schematic diagram of a bulk acoustic wave resonator according to a third example of the present disclosure. [Figure 9] 9 is a flowchart for manufacturing the bulk acoustic wave resonator shown in FIG. 8. [Figure 10] FIG. 10 is a schematic diagram of a bulk acoustic wave resonator according to a fourth example of the present disclosure. [Figure 11] 11 is a manufacturing flowchart of the bulk acoustic wave resonator shown in FIG. [Figure 12] FIG. 10 is a schematic diagram of a bulk acoustic wave resonator according to a fifth example of the present disclosure. [Figure 13] 13 is a manufacturing flowchart of the bulk acoustic wave resonator shown in FIG. 12. [Figure 14] FIG. 10 is a schematic diagram of a bulk acoustic wave resonator according to a sixth example of the present disclosure. [Figure 15] 15 is a manufacturing flow of the bulk acoustic wave resonator shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be described in detail below in combination with drawings and specific embodiments.

[0030] Unless otherwise defined, technical or scientific terms used in this disclosure have the common meaning as understood by a person of ordinary skill in the field to which this disclosure belongs. The terms "first," "second," and similar terms used in this disclosure do not denote any order, quantity, or importance, but are used only to distinguish between different components. Similarly, similar terms such as "one," "an," or "the" do not denote a quantitative limitation but indicate the presence of at least one. Similar terms such as "comprise," "contain," and similar terms mean that the element or item preceding the term encompasses the elements or items listed thereafter and their equivalents, but do not exclude other elements or items. Similar terms such as "connect" or "couple" are not limited to physical or mechanical connections, but may also include electrical connections, whether direct or indirect. Terms such as "top," "bottom," "left," and "right" are used only to denote relative positions, and if the absolute position of the described object is changed, the relative positions may also be changed accordingly.

[0031] As shown in Figures 1 to 3, in order to reduce insertion loss during the filtering process, bulk acoustic wave resonators must confine the acoustic signal as much as possible within the piezoelectric layer 12 between the first electrode 11 and the second electrode 13 and prevent the acoustic signal from diffusing to the outside. Therefore, acoustic wave reflectors are usually constructed on the top and bottom surfaces of the resonator. The top surface generally uses a low acoustic impedance air medium as the reflector, and depending on the construction of the acoustic wave reflector on the bottom surface, bulk acoustic wave resonators can be broadly divided into three types: back-etched bulk acoustic wave resonators as shown in Figure 1, film bulk acoustic resonators (abbreviated as FBAR) as shown in Figure 2, i.e., thin film bulk acoustic wave resonators, and solid-mounted resonators (abbreviated as SMR) as shown in Figure 3, i.e., solid-mounted bulk acoustic wave resonators. Here, the FBAR constructs a first groove portion 102 formed by etching in the first base substrate 10 as an air gap below the first electrode, the SMR constructs an acoustic mirror structure 15 formed by repeatedly stacking high acoustic impedance layers 151 and low acoustic impedance layers 152 below the first electrode 11, and the back-etching type constructs a first cavity 101 formed in the first base substrate 10 as an air layer below the first electrode 11 by deeply etching the back surface of the silicon substrate to form a cavity.

[0032] Current bulk acoustic wave resonators are only applicable to the frequency range of 1 GHz to 6 GHz, and cannot accommodate frequency bands greater than 6 GHz. To address this issue, in the embodiments of the present disclosure, the acoustic velocity of the piezoelectric layer material in the bulk acoustic wave resonator is 18,000 m / s or higher. For example, boron nitride, specifically hexagonal boron nitride, is used as the piezoelectric layer material. This material not only has piezoelectric properties, but also has a high acoustic velocity of 18,600 m / s, which is 64% higher than the acoustic velocity of conventional piezoelectric layer materials. Therefore, the bulk acoustic wave resonator in the embodiments of the present disclosure can be applied to a higher frequency range. Bulk acoustic wave resonators manufactured using this hexagonal boron nitride material have the advantages of low cost, high resonant frequency, small volume, low insertion loss, small in-band ripple, large out-of-band suppression, and good rectangularity, and are widely used in frequency bands above 1 GHz in the mobile communications field, especially in the frequency band >6 GHz to 30 GHz, to effectively filter low-frequency interference signals and their harmonics in terrestrial environments, thereby improving the signal quality of mobile communications.

[0033] Hereinafter, a bulk acoustic wave resonator and a manufacturing method thereof according to an embodiment of the present disclosure will be described using a combination of specific examples.

[0034] First Example: FIG. 4 is a schematic diagram of a bulk acoustic wave resonator according to a first example of the present disclosure. As shown in FIG. 4, the bulk acoustic wave resonator includes a first base substrate 10 and a first electrode 11, a piezoelectric layer 12, and a second electrode 13, which are sequentially disposed on the first base substrate 10. The orthogonal projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the first base substrate 10 at least partially overlap. A packaging layer 16 may be further provided on the side of the second electrode 13 away from the first base substrate 10. The first base substrate 10 has a first cavity 101 penetrating through it in its thickness direction. The first base substrate 10 has a first surface (top surface) and a second surface (bottom surface) that are disposed opposite each other in the thickness direction. The first cavity 101 has a first opening formed in the first surface and a second opening formed in the second surface. The first electrode 11 is provided on the first surface, and the orthogonal projection of the first electrode 11 on the plane in which the second surface is located covers the orthogonal projection of the first opening on the plane in which the second surface is located.

[0035] In addition to the above structure, the bulk acoustic wave resonator further includes a first connection electrode 17 connected to the first electrode 11 through a via hole penetrating the piezoelectric layer 12 and located in the same layer as the second electrode 13. In this case, a radio frequency signal is input from the upper left corner of FIG. 4 , converted into an acoustic signal by the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, propagates vertically in the piezoelectric layer 12, and is then transmitted to the interface between the first electrode 11 and the piezoelectric layer 12, where it is reconverted into a radio frequency signal by the piezoelectric effect and transmitted upward through the conductive through-hole in the lower right corner of the first electrode 11, finally reaching and transmitting to the upper right corner of the second electrode 13. The first cavity 101 below the resonator and the air space above it function as acoustic reflectors, which confine the acoustic signal within the resonator structure without dissipating it, thereby reducing resonator loss.

[0036] In this example, the material of the piezoelectric layer 12 is preferably hBN, but cBN (cubic boron nitride) and wBN (wurtzite boron nitride) may also be selected. Of course, the material of the piezoelectric layer 12 may also be AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO14, BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. The piezoelectric layer 12 in the embodiments of the present disclosure may be any of the above piezoelectric materials or may be a laminate of the above various piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10 nm to 100 μm.

[0037] The material of the first base substrate 10 is preferably glass, but materials such as Si, sapphire, SiC, GaAs, GaN, InP, BN, and ZnO may also be selected, and the thickness of the first base substrate 10 ranges from 0.1 μm to 10 mm.

[0038] The material of the first electrode 11 is preferably metallic Cu, because its lattice size is very close to that of hexagonal boron nitride (hBN). Other materials that may be used include Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and alloys of the above metals. The thickness of the first electrode 11 is in the range of 1 nm to 10 μm.

[0039] Materials that can be selected as the material for the second electrode 13 include Cu, Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and may also be alloy materials made of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0040] The material of the packaging layer 16 is preferably an organic compound that can block water vapor and oxygen gas, such as polyimide or epoxy resin, or an inorganic material such as SiNx or Al2O3. The packaging layer 16 may be a single layer of one type of material, or may be a laminate of multiple types of materials.

[0041] For the bulk acoustic wave resonator shown in FIG. 4 , an embodiment of the present disclosure provides a manufacturing method for the bulk acoustic wave resonator, and FIG. 5 is a manufacturing flowchart for the bulk acoustic wave resonator shown in FIG. 4 . As shown in FIG. 5 , the manufacturing method may specifically include the following steps:

[0042] Step S11: providing a first base substrate 10;

[0043] In this step, the first base substrate 10 may be cleaned and then dried by an air knife.

[0044] In step S12, the first electrode 11 is formed on the first base substrate 10.

[0045] In some examples, step S12 may include depositing a first conductive thin film on the first base substrate 10, preferably by DC magnetron sputtering (or RF magnetron sputtering), or by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or by attaching a copper foil. The first conductive film may be coated (or spray coated), pre-baked, exposed, developed, and post-baked. Finally, etching is performed, preferably by wet etching, or alternatively by dry etching, to form a pattern including the first electrode 11.

[0046] In step S13, the piezoelectric layer 12 is formed on the first substrate 10 after the above steps are completed.

[0047] In some examples, for example, hBN is used as the material for the piezoelectric layer 12. In step S13, oriented growth of the piezoelectric material can be performed first. RF magnetron sputtering is preferably used. The target is hBN. By controlling the Ar and N gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an oriented hBN thin film rich in nitrogen vacancies is formed (its piezoelectric properties are superior to those of BN without nitrogen vacancies). The growth orientation is preferably (100), but may also be (001) or (111). The thin film deposition method may be pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), or the like. The piezoelectric layer 12 is then subjected to photolithography, which includes coating (or spray coating), pre-baking, exposure, development, and post-baking. Finally, the piezoelectric material layer is etched to form a pattern of the piezoelectric layer 12 having the first connection via 121. A preferred etching technique may be a wet etching technique or a dry etching technique.

[0048] In step S14, the second electrodes 13 and the first connection electrodes 17 are formed on the first base substrate 10 after the above steps are completed.

[0049] In some examples, step S14 may include first depositing a second conductive thin film. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), but may also be pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. The second conductive thin film is sequentially coated (or spray coated), pre-baked, exposed, developed, and post-baked, and finally etched to form the second electrode 13 and the first connecting electrode 17. A wet etching technique is preferred, but a dry etching technique may also be selected. Because the second conductive thin film formed on the hole wall is thin and is unfavorable for low-loss transmission of radio frequency signals, electroplating may be performed to thicken the second conductive thin film in the first connecting via 121 before forming the patterns of the second electrode 13 and the first connecting electrode 17.

[0050] Step S15: forming a packaging layer 16 on the first base substrate 10 after the above steps are completed.

[0051] In some examples, the material of the packaging layer 16 may be an organic material, polyimide. In this case, step S15 may include liquid coating of the organic material, which may be performed by spin coating, spraying, inkjet printing, transfer printing, or the like, followed by heat curing to form the pattern of the packaging layer 16.

[0052] Step S16: A first cavity 101 is formed in the first base substrate 10 after the above steps are completed.

[0053] In some examples, the first base substrate 10 may be a glass substrate, in which case step S16 may include bombarding the first base substrate 10 using laser induction followed by HF etching to produce a first cavity 101 that penetrates the thickness of the first base substrate 10. The cross section of the first cavity 101 is approximately 90° perpendicular to the glass surface. For other non-glass substrates, the first cavity 101 may be formed using wet etching or dry etching.

[0054] Second Example: FIG. 6 is a schematic diagram of a bulk acoustic wave resonator according to a second example of the present disclosure. As shown in FIG. 6, the bulk acoustic wave resonator includes a first base substrate 10, a first electrode 11, a dielectric layer 18, a piezoelectric layer 12, and a second electrode 13, which are sequentially disposed on the first base substrate 10. A packaging layer 16 may be further disposed on the side of the second electrode 13 away from the first base substrate 10. The first base substrate 10 has a first cavity 101 penetrating through it in its thickness direction. The first base substrate 10 has a first surface (top surface) and a second surface (bottom surface) disposed opposite each other in its thickness direction. The first cavity 101 has a first opening formed in the first surface and a second opening formed in the second surface. The first electrode 11 is disposed on the first surface, and the orthogonal projection of the first electrode 11 on the plane where the second surface is located covers the orthogonal projection of the first opening on the plane where the second surface is located.

[0055] In addition to the above structure, the bulk acoustic wave resonator further includes a first connection electrode 17 connected to the first electrode 11 through a via hole penetrating the piezoelectric layer 12 and located in the same layer as the second electrode 13. In this case, a radio frequency signal is input from the upper left corner of FIG. 6, then converted into an acoustic signal by the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, and propagates vertically in the piezoelectric layer 12. When the radio frequency signal reaches the interface between the first electrode 11, the dielectric layer 18, and the piezoelectric layer 12, it is reconverted into a radio frequency signal by the piezoelectric effect and propagates upward through the conductive through-hole at the lower right corner of the first electrode 11, and finally reaches and propagates to the upper right corner of the second electrode 13. The first cavity 101 below the resonator and the air space above it function as acoustic reflectors, which confine the acoustic signal within the resonator structure without dissipating it, thereby reducing the loss of the resonator.

[0056] In this example, the material of the piezoelectric layer 12 is preferably hBN, but cBN or wBN may also be selected. Of course, the material of the piezoelectric layer 12 may also be selected from AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO14, BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, and the like. The piezoelectric layer 12 in the embodiments of the present disclosure may be any of the above piezoelectric materials or may be a laminate of the above various piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10 nm to 100 μm.

[0057] The material of the first base substrate 10 is preferably glass, but materials such as Si, sapphire, SiC, GaAs, GaN, InP, BN, and ZnO may also be selected, and the thickness of the first base substrate 10 ranges from 0.1 μm to 10 mm.

[0058] The material of the first electrode 11 is preferably metallic Cu, because its lattice size is very close to that of hexagonal boron nitride (hBN). Other materials that may be used include Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and alloys of the above metals. The thickness of the first electrode 11 is in the range of 1 nm to 10 μm.

[0059] The inductive layer 18 is located between the first electrode 11 and the piezoelectric layer 12. Its role is to assist the growth of the piezoelectric layer 12, to orient the piezoelectric layer 12 along the C-axis (the acoustic velocity along the C-axis of the piezoelectric layer 12 is the highest), and at the same time to improve the material quality of the piezoelectric layer 12 (for example, an X-ray diffraction rocking curve half-width of less than 1.5°). In this embodiment, the inductive layer 18 is preferably graphene, and may be single-layer graphene, bilayer graphene, or multilayer graphene. That is, the thickness range is 0.1 nm to 100 nm.

[0060] Materials that can be selected as the material for the second electrode 13 include Cu, Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and may also be alloy materials made of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0061] The material of the packaging layer 16 is preferably an organic compound that can block water vapor and oxygen gas, such as polyimide or epoxy resin. x Alternatively, inorganic materials such as Al2O3 may be selected. The packaging layer 16 may be a single layer of one type of material, or may be a laminate of multiple types of materials.

[0062] For the bulk acoustic wave resonator shown in FIG. 6 , an embodiment of the present disclosure provides a manufacturing method for the bulk acoustic wave resonator, and FIG. 7 is a manufacturing flowchart for the bulk acoustic wave resonator shown in FIG. 6 . As shown in FIG. 7 , the manufacturing method may specifically include the following steps:

[0063] Step S21: providing a first base substrate 10;

[0064] In this step, the first base substrate 10 may be cleaned and then dried by an air knife.

[0065] In step S22, the first electrode 11 is formed on the first base substrate 10.

[0066] In some examples, step S22 may include depositing a first conductive thin film on the first base substrate 10, preferably by DC magnetron sputtering (or RF magnetron sputtering), or by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or by attaching a copper foil. The first conductive film may be coated (or spray coated), pre-baked, exposed, developed, and post-baked. Finally, etching is performed, preferably by wet etching, or alternatively by dry etching, to form a pattern including the first electrode 11.

[0067] Step S23: forming an induction layer 18 on the first base substrate 10 after the above steps are completed.

[0068] In some examples, the material of the inductive layer 18 is preferably a graphene thin film, and may be a single layer, two layers, or multiple layers. For example, if the material of the first electrode 11 formed in step S22 is Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, or Au metal, or a Co-Ni or Au-Ni alloy, the inductive layer 18 may be graphene. For example, the inductive layer 18 may be directly grown by magnetron sputtering chemical vapor deposition or microwave plasma chemical vapor deposition. Specifically, a mixture of methane, nitrogen, and argon gas is introduced, the substrate is heated to 600-800°C, and a reaction occurs to form a graphene thin film. If the first electrode 11 formed in step S22 is not one of the above metals or alloys, the inductive layer may be formed in two steps: (a) the first step is the formation of a graphene thin film. Metal foils, such as Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, and Au metals, or Co-Ni and Au-Ni alloy foils, are placed in a reaction chamber and grown by magnetron sputtering or microwave plasma chemical vapor deposition. Specifically, a mixture of methane, nitrogen, and argon gas is introduced, and the substrate is heated to 600-800°C to form a graphene thin film. (b) The second step involves transferring the resulting graphene thin film from the metal foil to the first electrode 11. First, polymethyl methacrylate (PMMA) is sprayed or spin-coated onto the metal foil / graphene in an inert gas atmosphere, then dried and cured by heating at 120°C for 3-5 minutes. The metal foil / graphene / PMMA is then placed in the corresponding solution to dissolve the metal. For copper foil, a 20% FeCl3 solution is used. The remaining graphene / PMMA is floated on the surface of the solution, and the graphene / PMMA is removed and washed in deionized water. Then, the graphene / PMMA is transferred to the first electrode 11 and dried by irradiating it with an infrared lamp for 10 to 15 minutes. Finally, the PMMA is dissolved in an organic solvent, such as acetone, to complete the fabrication of the induction layer 18.

[0069] In step S24, the piezoelectric layer 12 is formed on the first base substrate 10 after the above steps are completed.

[0070] In some examples, for example, using hBN as the material for the piezoelectric layer 12, oriented growth of the piezoelectric material can be performed in step S24. RF magnetron sputtering is preferably used. The target is hBN. By controlling the Ar and N gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an oriented hBN thin film rich in nitrogen vacancies (whose piezoelectric properties are superior to those of BN without nitrogen vacancies) is formed. The growth orientation is preferably (100), but may also be (001) or (111). The thin film deposition method may be pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), or the like. The piezoelectric layer 12 is then subjected to photolithography, which includes coating (or spray coating), pre-baking, exposure, development, and post-baking. Finally, the piezoelectric material layer and the dielectric layer 18 are etched to form the first connection via 121, and the preferred etching technique may be a wet etching technique or a dry etching technique.

[0071] In step S25, the second electrodes 13 and the first connection electrodes 17 are formed on the first base substrate 10 after the above steps are completed.

[0072] In some examples, step S25 may include first depositing a second conductive thin film. The deposition method is preferably DC magnetron sputtering (or RF magnetron sputtering), but may also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. The second conductive thin film is sequentially coated (or spray coated), pre-baked, exposed, developed, and post-baked, and finally etched to form the second electrode 13 and the first connection electrode 17. A wet etching technique is preferred, but a dry etching technique may also be selected. Because the second conductive thin film formed on the hole wall is thin and disadvantageous for low-loss transmission of radio frequency signals, electroplating may be performed to thicken the second conductive thin film in the first connection via 121 before forming the second electrode 13 and the first connection pattern.

[0073] Step S26: forming a packaging layer 16 on the first base substrate 10 after the above steps are completed.

[0074] In some examples, the material of the packaging layer 16 may be an organic material, polyimide. In this case, step S26 may include liquid coating of the organic material, which may be performed by spin coating, spraying, inkjet printing, transfer printing, or the like, followed by heat curing to form the pattern of the packaging layer 16.

[0075] Step S27: The first cavity 101 is formed in the first base substrate 10 after the above steps are completed.

[0076] In some examples, the first base substrate 10 may be a glass substrate, in which case step S27 may include bombarding the first base substrate 10 using laser induction followed by HF etching to produce a first cavity 101 that penetrates the thickness of the first base substrate 10. The cross section of the first cavity 101 is approximately 90° perpendicular to the glass surface. For other non-glass substrates, the first cavity 101 may be formed using wet etching or dry etching.

[0077] Third Example: FIG. 8 is a schematic diagram of a bulk acoustic wave resonator according to a third example of the present disclosure. As shown in FIG. 8, the bulk acoustic wave resonator includes a first base substrate 10, a separation layer 14, a first electrode 11, a piezoelectric layer 12, and a second electrode 13, which are sequentially provided on the first base substrate 10. A packaging layer 16 may be further provided on the side of the second electrode 13 away from the first base substrate 10. Here, the first base substrate 10 has a first groove 102. The first base substrate 10 has a first surface (upper surface) and a second surface (lower surface) that are provided opposite each other in the thickness direction. The third opening of the first groove 102 is located on the first surface, the first electrode 11 is provided on the first surface, and the orthogonal projection of the second surface of the first electrode 11 on a plane where the second surface is located covers the orthogonal projection of the second surface of the third opening on a plane where the second surface is located.

[0078] In addition to the above structure, the bulk acoustic wave resonator further includes a first connection electrode 17 connected to the first electrode 11 through a via hole penetrating the piezoelectric layer 12 and located in the same layer as the second electrode 13. In this case, a radio frequency signal is input from the upper left corner of FIG. 8, converted into an acoustic signal by the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, propagates vertically in the piezoelectric layer 12, and when transmitted to the interface between the first electrode 11 and the piezoelectric layer 12, converted back into a radio frequency signal by the piezoelectric effect and transmitted upward through the conductive through-hole in the lower right corner of the first electrode 11, finally reaching and transmitting to the upper right corner of the second electrode 13. The first groove 102 below the resonator and the air space above it function as acoustic reflectors, which confine the acoustic signal within the resonator structure without dissipating it, thereby reducing resonator loss.

[0079] In this example, the material of the piezoelectric layer 12 is preferably hBN, but cBN or wBN may also be selected. Of course, the material of the piezoelectric layer 12 may also be selected from AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO14, BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, and the like. The piezoelectric layer 12 in the embodiments of the present disclosure may be any of the above piezoelectric materials or may be a laminate of the above various piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10 nm to 100 μm.

[0080] The material of the first base substrate 10 is preferably glass, but materials such as Si, sapphire, SiC, GaAs, GaN, InP, BN, and ZnO may also be selected, and the thickness of the first base substrate 10 ranges from 0.1 μm to 10 mm.

[0081] The isolation layer 14 electrically isolates the first groove portion 102 from the bulk acoustic wave resonator and also provides structural support. Selectable insulating materials include SiO2, Si3N4, Al2O3, and laminates thereof. The thickness ranges from 1 nm to 100 μm.

[0082] The material of the first electrode 11 is preferably metallic Cu, because its lattice size is very close to that of hexagonal boron nitride (hBN). Other materials that may be used include Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and alloys of the above metals. The thickness of the first electrode 11 is in the range of 1 nm to 10 μm.

[0083] Materials that can be selected as the material for the second electrode 13 include Cu, Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and may also be alloy materials made of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0084] The material of the packaging layer 16 is preferably an organic compound that can block water vapor and oxygen gas, such as polyimide or epoxy resin. x Alternatively, inorganic materials such as Al2O3 may be selected. The packaging layer 16 may be a single layer of one type of material, or may be a laminate of multiple materials.

[0085] For the bulk acoustic wave resonator shown in FIG. 8 , an embodiment of the present disclosure provides a manufacturing method for the bulk acoustic wave resonator, and FIG. 9 is a manufacturing flowchart for the bulk acoustic wave resonator shown in FIG. 8 . As shown in FIG. 9 , the manufacturing method may specifically include the following steps:

[0086] Step S31: providing a first base substrate 10;

[0087] In this step, the first base substrate 10 may be cleaned and then dried by an air knife.

[0088] In step S32, the first groove portion 102 is formed in the first base substrate 10.

[0089] In some examples, step S32 may include first depositing a mask material on the first base substrate 10 (selectable mask materials include photoresist, an inorganic mask, or a metal mask), followed by coating (or spray coating), pre-baking, exposure, development, post-baking, and finally etching to form a mask. The etching technique may be either dry etching or wet etching, with wet etching being preferred. Next, the first base substrate 10 is etched to form the first groove portion 102. The etching technique may be either wet etching or dry etching, with wet etching being preferred. For example, the first base substrate 10 is a glass substrate, and the etching solution used here is a mixed solution of 3% to 7% hydrofluoric acid, 20% to 30% ammonium fluoride, and deionized water.

[0090] Step S33: forming a filling structure 19 in the first groove portion 102 to fill and flatten the first groove portion 102;

[0091] In this step, the first groove portion 102 formed in step S32 is first filled and flattened to ensure smooth subsequent processes. Here, the material of the filling structure 19 is preferably hydrophobic silica doped with boron and phosphorus. In some examples, step S33 involves obtaining a slurry containing boron- and phosphorus-doped hydrophobic silica by plasma-enhanced chemical vapor deposition (PECVD), secondary atmospheric pressure chemical vapor deposition (SACVD), or screen printing, followed by thermal annealing at 700°C to 900°C to liquefy and flow the hydrophobic boron- and phosphorus-doped silica thin film, completely filling the pores in the first groove portion 102, followed by cooling and curing. Next, electrochemical mechanical polishing (CMP) is performed to remove the boron- and phosphorus-doped silica thin film above the substrate surface, and polishing the first surface of the first base substrate 10.

[0092] In step S34, the separation layer 14 and the first electrode 11 are formed on the first base substrate 10 after the above steps are completed, and the first through-hole 20 penetrating the separation layer 14 and the first electrode 11 is formed.

[0093] In some examples, step S34 may include first depositing an electrically insulating material, the deposition method of which may be selected from RF-controlled sputtering, pulsed laser sputtering (PLD), atomic layer deposition (ALD), and plasma-enhanced chemical vapor deposition (PECVD), followed by coating (or spray coating), pre-baking, exposure, development, post-baking, and etching to form the isolation layer 14. Here, the etching technique may be a wet etching technique or a dry etching technique.

[0094] In step S35, a first conductive thin film is formed on the side of the isolation layer 14 away from the first base substrate 10. The deposition method is preferably DC magnetron sputtering (or RF magnetron sputtering), but may also be pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or a copper foil attachment method. The first conductive film is then coated (or spray coated), pre-baked, exposed, developed, and post-baked. Finally, etching is performed, preferably wet etching, or alternatively dry etching, to form a pattern including the first electrode 11.

[0095] Finally, the separation layer 14 and the first electrode 11 are etched to form the first through-hole 20. Here, the number of the first through-hole 20 may be one or more, and in the embodiment of the present disclosure, the number of the first through-holes 20 is preferably more than one. Specifically, on the side of the first electrode 11 away from the first base substrate 10, coating (or spray coating), pre-baking, exposure, development, and post-baking are performed, and then the first electrode 11 is first dry-etched, and then the etching gas is exchanged and the separation layer 14 is etched down to the filler material layer.

[0096] In step S36, the piezoelectric layer 12 is formed on the first base substrate 10 after the above steps are completed.

[0097] In some examples, for example, using hBN as the material for the piezoelectric layer 12, oriented growth of the piezoelectric material can be performed in step S36. RF magnetron sputtering is preferably used. The target is hBN. By controlling the Ar and N gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an oriented hBN thin film rich in nitrogen vacancies (whose piezoelectric properties are superior to those of BN without nitrogen vacancies) is formed. The growth orientation is preferably (100), but may also be (001) or (111). The thin film deposition method may be pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), or the like. The piezoelectric layer 12 is then subjected to photolithography, which includes coating (or spray coating), pre-baking, exposure, development, and post-baking. Finally, the piezoelectric material layer is etched to form a pattern of the piezoelectric layer 12 having the first connection vias 121, and the preferred etching technique may be a wet etching technique or a dry etching technique.

[0098] In step S37, the second electrodes 13 and the first connection electrodes 17 are formed on the first base substrate 10 after the above steps are completed.

[0099] In some examples, step S37 may include first depositing a second conductive thin film, preferably by DC magnetron sputtering (or RF magnetron sputtering), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, or electron beam evaporation. The second conductive thin film is sequentially coated (or spray coated), pre-baked, exposed, developed, and post-baked, and finally etched to form the second electrode 13 and the first connection electrode 17, preferably by wet etching or alternatively by dry etching. Because the second conductive thin film formed on the hole wall is thin and unfavorable for low-loss transmission of radio frequency signals, electroplating may be performed to thicken the second conductive thin film in the first connection via 121 before forming the second electrode 13 and the first connection pattern.

[0100] In step S38, the filling structure 19 is removed.

[0101] In some examples, step S38 may include immersion etching using a mixture of hydrofluoric acid and nitric acid for a sufficient period of time to completely dissolve the boron and phosphorus doped silica filler material in the first trench 102, and finally rinsing the first trench 102 with deionized water and drying.

[0102] Fourth Example: FIG. 10 is a schematic diagram of a bulk acoustic wave resonator according to a fourth example of the present disclosure. As shown in FIG. 10, the bulk acoustic wave resonator includes a first base substrate 10, a separation layer 14, a first electrode 11, a dielectric layer 18, a piezoelectric layer 12, and a second electrode 13, which are sequentially provided on the first base substrate 10. A packaging layer 16 may be further provided on the side of the second electrode 13 away from the first base substrate 10. Here, the first base substrate 10 has a first groove 102. The first base substrate 10 has a first surface (upper surface) and a second surface (lower surface) that are provided opposite each other in the thickness direction. The third opening of the first groove 102 is located on the first surface, the first electrode 11 is provided on the first surface, and the orthogonal projection of the first electrode 11 on a plane on which the second surface is located covers the orthogonal projection of the third opening on a plane on which the second surface is located.

[0103] Furthermore, the bulk acoustic wave resonator not only includes the above structure but also a first connection electrode 17 connected to the first electrode 11 through a via that penetrates the piezoelectric layer 12 and disposed in the same layer as the second electrode 13. In this case, a radio frequency signal is input from the upper left corner of FIG. 10 , then converted into an acoustic signal by the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, and propagates vertically in the piezoelectric layer 12. When the radio frequency signal reaches the interface between the first electrode 11, the dielectric layer 18, and the piezoelectric layer 12, it is reconverted into a radio frequency signal by the piezoelectric effect and transmitted upward through the conductive through-hole in the lower right corner of the first electrode 11, and finally reaches and is transmitted to the upper right corner of the second electrode 13. The first groove 102 below the resonator and the air space above it function as acoustic reflectors, which confine the acoustic signal within the resonator structure without dissipating it, thereby reducing resonator loss.

[0104] In this example, the material of the piezoelectric layer 12 is preferably hBN, but cBN or wBN may also be selected. Of course, the material of the piezoelectric layer 12 may also be selected from AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO14, BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, and the like. The piezoelectric layer 12 in the embodiments of the present disclosure may be any of the above piezoelectric materials or may be a laminate of the above various piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10 nm to 100 μm.

[0105] The material of the first base substrate 10 is preferably glass, but materials such as Si, sapphire, SiC, GaAs, GaN, InP, BN, and ZnO may also be selected, and the thickness of the first base substrate 10 ranges from 0.1 μm to 10 mm.

[0106] The isolation layer 14 electrically isolates the first groove portion 102 from the bulk acoustic wave resonator and also provides structural support. Selectable insulating materials include SiO2, Si3N4, Al2O3, and laminates thereof. The thickness ranges from 1 nm to 100 μm.

[0107] The material of the first electrode 11 is preferably metallic Cu, because its lattice size is very close to that of hexagonal boron nitride (hBN). Other materials that may be used include Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and alloys of the above metals. The thickness of the first electrode 11 is in the range of 1 nm to 10 μm.

[0108] The inductive layer 18 is located between the first electrode 11 and the piezoelectric layer 12. Its role is to assist the growth of the piezoelectric layer 12, to orient the piezoelectric layer 12 along the C-axis (the acoustic velocity along the C-axis of the piezoelectric layer 12 is the highest), and at the same time to improve the material quality of the piezoelectric layer 12 (for example, an X-ray diffraction rocking curve half-width of less than 1.5°). In this embodiment, the inductive layer 18 is preferably graphene, and may be single-layer graphene, bilayer graphene, or multilayer graphene. That is, the thickness range is 0.1 nm to 100 nm.

[0109] Materials that can be selected as the material for the second electrode 13 include Cu, Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and may also be alloy materials made of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0110] The material of the packaging layer 16 is preferably an organic compound that can block water vapor and oxygen gas, such as polyimide or epoxy resin. x Alternatively, inorganic materials such as Al2O3 may be selected. The packaging layer 16 may be a single layer of one type of material, or may be a laminate of multiple materials.

[0111] For the bulk acoustic wave resonator shown in FIG. 10 , an embodiment of the present disclosure provides a manufacturing method for the bulk acoustic wave resonator, and FIG. 11 is a manufacturing flowchart for the bulk acoustic wave resonator shown in FIG. 10 . As shown in FIG. 11 , the manufacturing method may specifically include the following steps:

[0112] Step S41: providing a first base substrate 10;

[0113] In this step, the first base substrate 10 may be cleaned and then dried by an air knife.

[0114] In step S42, the first groove portion 102 is formed in the first base substrate 10.

[0115] In some examples, step S42 may include first depositing a mask material on the first base substrate 10 (selectable mask materials include photoresist, an inorganic mask, or a metal mask), followed by coating (or spray coating), pre-baking, exposure, development, post-baking, and finally etching to form a mask. The etching technique may be either dry etching or wet etching, with wet etching being preferred. Next, the first base substrate 10 is etched to form the first groove portion 102. The etching technique may be either wet etching or dry etching, with wet etching being preferred. For example, the first base substrate 10 is a glass substrate, and the etching solution used here is a mixed solution of 3% to 7% hydrofluoric acid, 20% to 30% ammonium fluoride, and deionized water.

[0116] Step S43: forming a filling structure 19 in the first groove portion 102 to fill and flatten the first groove portion 102;

[0117] In this step, the first groove portion 102 formed in step S42 is first filled and flattened to ensure smooth subsequent processes. Here, the material of the filling structure 19 is preferably hydrophobic silica doped with boron and phosphorus. In some examples, step S43 involves obtaining a slurry containing boron- and phosphorus-doped hydrophobic silica by plasma-enhanced chemical vapor deposition (PECVD), secondary atmospheric pressure chemical vapor deposition (SACVD), or screen printing, followed by thermal annealing at 700°C to 900°C to liquefy and flow the hydrophobic boron- and phosphorus-doped silica thin film, completely filling the pores in the first groove portion 102, followed by cooling and curing. Next, electrochemical mechanical polishing (CMP) is performed to remove the boron- and phosphorus-doped silica thin film above the substrate surface, and polishing the first surface of the first base substrate 10.

[0118] In step S44, the separation layer 14 and the first electrode 11 are formed on the first base substrate 10 after the above steps are completed.

[0119] In some examples, step S44 may include first depositing an electrically insulating material, the deposition method of which may be selected from RF-controlled sputtering, pulsed laser sputtering (PLD), atomic layer deposition (ALD), and plasma-enhanced chemical vapor deposition (PECVD), followed by coating (or spray coating), pre-baking, exposure, development, post-baking, and etching to form the isolation layer 14. Here, the etching technique may be a wet etching technique or a dry etching technique.

[0120] Next, a first conductive thin film is formed on the side of the isolation layer 14 away from the first base substrate 10. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), but methods such as pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, and electron beam evaporation may also be selected, or a copper foil may be attached. The first conductive film is then coated (or spray coated), pre-baked, exposed, developed, and post-baked. Finally, etching is performed, preferably wet etching, or alternatively dry etching, to form a pattern including the first electrode 11.

[0121] In step S45, an induction layer 18 is formed on the first base substrate 10 after the above steps are completed, and the separation layer 14 and the first electrode 11 are etched to form the first through-holes 20.

[0122] In some examples, the material of the inductive layer 18 is preferably a graphene thin film, and may be a single layer, two layers, or multiple layers. For example, if the material of the first electrode 11 formed in step S44 is Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, or Au metal, or a Co-Ni or Au-Ni alloy, the inductive layer 18 may be graphene material. For example, the inductive layer 18 may be directly grown by magnetron sputtering chemical vapor deposition or microwave plasma chemical vapor deposition. Specifically, a mixture of methane, nitrogen, and argon gas is introduced, the substrate is heated to 600-800°C, and a reaction occurs to form a graphene thin film. If the first electrode 11 formed in step S44 is not one of the above metals or alloys, the inductive layer may be formed in two steps: (a) the first step is the formation of a graphene thin film. Metal foils, such as Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, and Au metals, or Co-Ni and Au-Ni alloy foils, are placed in a reaction chamber and grown by magnetron sputtering or microwave plasma chemical vapor deposition. Specifically, a mixture of methane, nitrogen, and argon gas is introduced, and the substrate is heated to 600-800°C to form a graphene thin film. (b) The second step involves transferring the resulting graphene thin film from the metal foil to the first electrode 11. First, polymethyl methacrylate (PMMA) is sprayed or spin-coated onto the metal foil / graphene in an inert gas atmosphere, then dried and cured by heating at 120°C for 3-5 minutes. The metal foil / graphene / PMMA is then placed in the corresponding solution to dissolve the metal. For copper foil, a 20% FeCl3 solution is used. The remaining graphene / PMMA is floated on the surface of the solution, and the graphene / PMMA is removed and washed in deionized water. Then, the graphene / PMMA is transferred to the first electrode 11 and dried by irradiating it with an infrared lamp for 10 to 15 minutes. Finally, the PMMA is dissolved in an organic solvent, such as acetone, to complete the fabrication of the induction layer 18.

[0123] Finally, the separation layer 14 and the first electrode 11 on the first base substrate 10 are etched to form the first through-holes 20 .

[0124] Here, the number of first through holes 20 may be one or more, and preferably, in the embodiments of the present disclosure, the number of first through holes 20 is more than one. In some examples, step S37 may include coating (or spray coating), pre-baking, exposing, developing, and post-baking the side of first electrode 11 away from first base substrate 10, and then first dry etching first electrode 11, and then exchanging the etching gas to etch separation layer 14 down to the fill material layer.

[0125] In step S46, the piezoelectric layer 12 is formed on the first base substrate 10 after the above steps are completed.

[0126] In some examples, for example, using hBN as the material for the piezoelectric layer 12, oriented growth of the piezoelectric material can be performed in step S46. RF magnetron sputtering is preferably used. The target is hBN. By controlling the Ar and N gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an oriented hBN thin film rich in nitrogen vacancies is formed (whose piezoelectric properties are superior to those of BN without nitrogen vacancies). The growth orientation is preferably (100), but may also be (001) or (111). The thin film deposition method may be pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), or the like. The piezoelectric layer 12 is then subjected to photolithography, which includes coating (or spray coating), pre-baking, exposure, development, and post-baking. Finally, the piezoelectric material layer is etched to form a pattern of the piezoelectric layer 12 having the first connection vias 121, and the preferred etching technique may be a wet etching technique or a dry etching technique.

[0127] In step S47, the second electrodes 13 and the first connection electrodes 17 are formed on the first base substrate 10 after the above steps are completed.

[0128] In some examples, step S47 may include first depositing a second conductive thin film, preferably by DC magnetron sputtering (or RF magnetron sputtering), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, or electron beam evaporation. The second conductive thin film is sequentially coated (or spray coated), pre-baked, exposed, developed, and post-baked, and finally etched to form the second electrode 13 and the first connection electrode 17, preferably by wet etching or alternatively by dry etching. Because the second conductive thin film formed on the hole wall is thin and unfavorable for low-loss transmission of radio frequency signals, electroplating may be performed to thicken the second conductive thin film in the first connection via 121 before forming the second electrode 13 and the first connection pattern.

[0129] In step S48, the filling structure 19 is removed.

[0130] In some examples, step S48 may include immersion etching using a mixture of hydrofluoric acid and nitric acid for a sufficient period of time to completely dissolve the boron and phosphorus doped silica filler material in the first trench 102, and finally rinsing the first trench 102 with deionized water and drying.

[0131] Fifth Example: FIG. 12 is a schematic diagram of a bulk acoustic wave resonator according to a fifth example of the present disclosure. As shown in FIG. 12, the bulk acoustic wave resonator includes a first base substrate 10, at least one acoustic mirror structure 15 sequentially disposed on the first base substrate 10, a first electrode 11, a piezoelectric layer 12, and a second electrode 13. A packaging layer 16 may be further provided on the side of the second electrode 13 away from the first base substrate 10. Here, the mirror structure 15 includes a first sub-structure layer and a second sub-structure layer sequentially disposed in a direction away from the first base substrate 10, and the acoustic impedance of the material of the first sub-structure layer is greater than the acoustic impedance of the material of the second sub-structure layer. For ease of explanation and understanding, the first sub-structure layer will be referred to as a high acoustic impedance layer 151, and the second sub-structure layer will be referred to as a low acoustic impedance layer 152.

[0132] In addition to the above structure, the bulk acoustic wave resonator further includes a first connection electrode 17 connected to the first electrode 11 through a via hole penetrating the piezoelectric layer 12 and located in the same layer as the second electrode 13. In this case, a radio frequency signal is input from the upper left corner of FIG. 12 , converted into an acoustic signal by the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, propagates vertically in the piezoelectric layer 12, and when transmitted to the interface between the first electrode 11 and the piezoelectric layer 12, converted back into a radio frequency signal by the piezoelectric effect, transmitted upward through the conductive through-hole in the lower right corner of the first electrode 11, and finally reaches and is transmitted to the upper right corner of the second electrode 13. The acoustic mirror structure 15 below the resonator and the air space above it function as acoustic reflectors, which confine the acoustic signal within the resonator structure without dissipating it, thereby reducing resonator loss.

[0133] In this example, the material of the piezoelectric layer 12 is preferably hBN, but cBN or wBN may also be selected. Of course, the material of the piezoelectric layer 12 may also be AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO14, BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, or other materials. The piezoelectric layer 12 in the present embodiment may be any of the above piezoelectric materials or may be a laminate of the above various piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10 nm to 100 μm.

[0134] The material of the first base substrate 10 is preferably glass, but materials such as Si, sapphire, SiC, GaAs, GaN, InP, BN, and ZnO may also be selected, and the thickness of the first base substrate 10 ranges from 0.1 μm to 10 mm.

[0135] The acoustic mirror structure 15 is configured by arranging high acoustic impedance layers 151 and low acoustic impedance layers 152. The acoustic impedance of a material is equal to the propagation speed of acoustic waves in the material multiplied by the density of the material. Theoretically, if the thickness of the high acoustic impedance layer 151 is equal to one-fourth the wavelength of an acoustic wave at the resonant frequency of the bulk acoustic wave resonator propagating in the high acoustic impedance layer 151, and the thickness of the low acoustic impedance layer 152 is equal to one-fourth the wavelength of an acoustic wave at the resonant frequency of the bulk acoustic wave resonator propagating in the low acoustic impedance layer 152, the effect of the alternating arrangement of the high and low acoustic impedance layers 152 (which may be high / low / high / low... or low / high / low / high...) is equivalent to an acoustic mirror, whose role is to reflect back acoustic signals leaking from above. The high acoustic impedance layer 151 and the low acoustic impedance layer 152 form a mirror structure 15. Generally, three to four pairs are sufficient to achieve a good acoustic reflection effect; of course, the more pairs, the better, but the higher the cost. The number of pairs is not limited here; the mirror structure 15 may have between one and 100 layers. There is no restriction on the thickness, whether it is equal to a quarter of the wavelength or not; any thickness is acceptable. Materials for the high acoustic impedance layer 151 may include W, Ir, Pt, Ru, Au, Mo, Ta, Ti, Cu, Ni, Zn, Al, Al2O3, Ag, etc.; typical low acoustic impedance materials may include SiO2, Si3N4, Mg, rubber, nylon, polyimide, polyethylene, polystyrene, Teflon, etc. Depending on the resonant frequency and the sound velocity of different materials, the thickness of the single-layer high acoustic impedance layer 151 and the single-layer low acoustic impedance layer 152 ranges from 1 nm to 10 μm.

[0136] The material of the first electrode 11 is preferably metallic Cu, because its lattice size is very close to that of hexagonal boron nitride (hBN). Other materials that may be used include Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and alloys of the above metals. The thickness of the first electrode 11 is in the range of 1 nm to 10 μm.

[0137] Materials that can be selected as the material for the second electrode 13 include Cu, Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and may also be alloy materials made of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0138] The material of the packaging layer 16 is preferably an organic compound that can block water vapor and oxygen gas, such as polyimide or epoxy resin. x Alternatively, inorganic materials such as Al2O3 may be selected. The packaging layer 16 may be a single layer of one type of material, or may be a laminate of multiple materials.

[0139] For the bulk acoustic wave resonator shown in FIG. 12 , an embodiment of the present disclosure provides a manufacturing method for the bulk acoustic wave resonator, and FIG. 13 is a manufacturing flowchart for the bulk acoustic wave resonator shown in FIG. 12 . As shown in FIG. 13 , the manufacturing method may specifically include the following steps:

[0140] Step S51: providing a first base substrate 10;

[0141] In this step, the first base substrate 10 may be cleaned and then dried by an air knife.

[0142] Step S52: fabricating the acoustic mirror structure 15 on the first base substrate 10;

[0143] In some examples, step S52 may include the following steps (a) and (b). (a) First, a thin-film material for the high acoustic impedance layer 151 is deposited. The deposition method is preferably DC magnetron sputtering (or may be RF magnetron sputtering), and may be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. Then, the thin film for the high acoustic impedance layer 151 is coated (or spray coated), pre-baked, exposed to light, developed, post-baked, and etched to form the high acoustic impedance layer 151. Here, the etching method is preferably wet etching, and may be dry etching. (b) A thin-film material for the low acoustic impedance layer 152 is further deposited. The deposition method is preferably DC magnetron sputtering (or may be RF magnetron sputtering), and may be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. Then, the low acoustic impedance layer 152 is formed by coating (or spray coating), pre-baking, exposing, developing, post-baking, and etching the thin film of the low acoustic impedance layer 152. Here, wet etching is preferable as the etching technique, but dry etching may also be selected. Then, steps (a) and (b) are repeated until an acoustic mirror structure 15 satisfying the number of layers required by the design is obtained.

[0144] In step S53, the first electrode 11 is formed on the first base substrate 10 after the above steps are completed.

[0145] In some examples, step S53 may include depositing a first conductive thin film on the first base substrate 10. The deposition method is preferably DC magnetron sputtering (or RF magnetron sputtering), but may also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or the like, or may be a copper foil attachment method. The first conductive film may be coated (or spray coated), pre-baked, exposed, developed, and post-baked. Finally, etching is performed, preferably wet etching, or alternatively dry etching, to form a pattern including the first electrode 11.

[0146] In step S54, the piezoelectric layer 12 is formed on the first base substrate 10 after the above steps are completed.

[0147] In some examples, for example, using hBN as the material for the piezoelectric layer 12, oriented growth of the piezoelectric material can be performed in step S54. RF magnetron sputtering is preferably used. The target is hBN. By controlling the Ar and N gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an oriented hBN thin film rich in nitrogen vacancies is formed (its piezoelectric properties are superior to those of BN without nitrogen vacancies). The growth orientation is preferably (100), but may also be (001) or (111). The thin film deposition method may be pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), or the like. The piezoelectric layer 12 is then subjected to photolithography, which includes coating (or spray coating), pre-baking, exposure, development, and post-baking. Finally, the piezoelectric material layer is etched to form a pattern of the piezoelectric layer 12 having the first connection via 121. A preferred etching technique may be a wet etching technique or a dry etching technique.

[0148] In step S55, the second electrodes 13 and the first connection electrodes 17 are formed on the first base substrate 10 after the above steps are completed.

[0149] In some examples, step S55 may include first depositing a second conductive thin film. The deposition method is preferably DC magnetron sputtering (or RF magnetron sputtering), but may also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. The second conductive thin film is sequentially coated (or spray coated), pre-baked, exposed, developed, and post-baked, and finally etched to form the second electrode 13 and the first connection electrode 17. A wet etching technique is preferred, but a dry etching technique may also be selected. Because the second conductive thin film formed on the hole wall is thin and disadvantageous for low-loss transmission of radio frequency signals, electroplating may be performed to thicken the second conductive thin film in the first connection via 121 before forming the second electrode 13 and the first connection pattern.

[0150] Step S56: forming a packaging layer 16 on the first base substrate 10 after the above steps are completed.

[0151] In some examples, the material of the packaging layer 16 may be an organic material, polyimide. In this case, step S56 may include liquid coating of the organic material, which may be performed by spin coating, spraying, inkjet printing, transfer printing, or the like, followed by heat curing to form the pattern of the packaging layer 16.

[0152] Sixth Example: FIG. 14 is a schematic diagram of a bulk acoustic wave resonator according to a sixth example of the present disclosure. As shown in FIG. 14, the bulk acoustic wave resonator includes a first base substrate 10, at least one acoustic mirror structure 15 sequentially disposed on the first base substrate 10, a first electrode 11, a dielectric layer 18, a piezoelectric layer 12, and a second electrode 13. A packaging layer 16 may be further provided on the side of the second electrode 13 away from the first base substrate 10. Here, the mirror structure 15 includes a first substructure and a second substructure sequentially disposed in a direction away from the first base 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 explanation and understanding, the first substructure will be referred to as a high acoustic impedance layer 151, and the second substructure will be referred to as a low acoustic impedance layer 152.

[0153] In addition to the above structure, the bulk acoustic wave resonator further includes a first connection electrode 17 connected to the first electrode 11 through a via hole penetrating the piezoelectric layer 12 and located in the same layer as the second electrode 13. In this case, a radio frequency signal is input from the upper left corner of FIG. 14, converted into an acoustic signal by the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, propagates vertically in the piezoelectric layer 12, and is then transmitted to the interface between the first electrode 11, the dielectric layer 18, and the piezoelectric layer 12, where it is reconverted into a radio frequency signal by the piezoelectric effect and transmitted upward through the conductive through-hole in the lower right corner of the first electrode 11, and finally reaches and is transmitted to the upper right corner of the second electrode 13. The acoustic mirror structure 15 below the resonator and the air space above it function as acoustic reflectors, which confine the acoustic signal within the resonator structure without dissipating it, thereby reducing resonator loss.

[0154] In this example, the material of the piezoelectric layer 12 is preferably hBN, but cBN or wBN may also be selected. Of course, the material of the piezoelectric layer 12 may also be AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO14, BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, or other materials. The piezoelectric layer 12 in this example may be any of the above piezoelectric materials or may be a laminate of the above various piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10 nm to 100 μm.

[0155] The material of the first base substrate 10 is preferably glass, but materials such as Si, sapphire, SiC, GaAs, GaN, InP, BN, and ZnO may also be selected, and the thickness of the first base substrate 10 ranges from 0.1 μm to 10 mm.

[0156] The acoustic mirror structure 15 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 propagation speed of acoustic waves in the material multiplied by the density of the material. Theoretically, if the thickness of the high acoustic impedance layer 151 is equal to one-fourth the wavelength of an acoustic wave at the resonant frequency of the bulk acoustic wave resonator propagating in the high acoustic impedance layer 151, and the thickness of the low acoustic impedance layer 152 is equal to one-fourth the wavelength of an acoustic wave at the resonant frequency of the bulk acoustic wave resonator propagating in the low acoustic impedance layer 152, the effect of the alternating arrangement of the high and low acoustic impedance layers 152 (which may be high / low / high / low... or low / high / low / high...) is equivalent to an acoustic mirror, whose role is to reflect back acoustic signals leaking from above. The high acoustic impedance layer 151 and the low acoustic impedance layer 152 form a mirror structure 15. Generally, three to four pairs are sufficient to achieve a good acoustic reflection effect; of course, the more pairs, the better, but the higher the cost. The number of pairs is not limited here; the mirror structure 15 may have between one and 100 layers. There is no restriction on the thickness, whether it is equal to a quarter of the wavelength or not; any thickness is acceptable. Materials for the high acoustic impedance layer 151 include W, Ir, Pt, Ru, Au, Mo, Ta, Ti, Cu, Ni, Zn, Al, Al2O3, and Ag. Typical low acoustic impedance materials include SiO2, Si3N4, Mg, rubber, nylon, polyimide, polyethylene, polystyrene, and Teflon. Depending on the resonant frequency and the sound velocity of different materials, the thickness of the single-layer high acoustic impedance layer 151 and the single-layer low acoustic impedance layer 152 ranges from 1 nm to 10 μm.

[0157] The material of the first electrode 11 is preferably metallic Cu, because its lattice size is very close to that of hexagonal boron nitride (hBN). Other materials that may be used include Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and alloys of these metals. The thickness of the first electrode 11 is in the range of 1 nm to 10 μm.

[0158] The inductive layer 18 is located between the first electrode 11 and the piezoelectric layer 12. Its role is to assist the growth of the piezoelectric layer 12, to orient the piezoelectric layer 12 along the C-axis (the acoustic velocity along the C-axis of the piezoelectric layer 12 is the highest), and at the same time, to improve the material quality of the piezoelectric layer 12 (for example, an X-ray diffraction rocking curve half-width of less than 1.5°). In this embodiment, the inductive layer 18 is preferably graphene, and may be single-layer graphene, bilayer graphene, or multilayer graphene. That is, the thickness range is 0.1 nm to 100 nm.

[0159] Materials that can be selected as the material for the second electrode 13 include Cu, Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au, and may also be alloy materials made of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0160] The material of the packaging layer 16 is preferably an organic compound that can block water vapor and oxygen gas, such as polyimide or epoxy resin. x Alternatively, inorganic materials such as Al2O3 may be selected. The packaging layer 16 may be a single layer of one type of material, or may be a laminate of multiple materials.

[0161] For the bulk acoustic wave resonator shown in FIG. 14 , an embodiment of the present disclosure provides a manufacturing method for the bulk acoustic wave resonator, and FIG. 15 shows a manufacturing flow of the bulk acoustic wave resonator shown in FIG. 14 . As shown in FIG. 15 , the manufacturing method may specifically include the following steps:

[0162] Step S61: providing a first base substrate 10;

[0163] In this step, the first base substrate 10 may be cleaned and then dried by an air knife.

[0164] Step S62: fabricating the acoustic mirror structure 15 on the first base substrate 10;

[0165] In some examples, step S62 may include the following steps (a) and (b). (a) First, a thin-film material for the high acoustic impedance layer 151 is deposited. The deposition method is preferably DC magnetron sputtering (or may be RF magnetron sputtering), and may be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. Then, the thin film for the high acoustic impedance layer 151 is coated (or spray coated), pre-baked, exposed to light, developed, post-baked, and etched to form the high acoustic impedance layer 151. Here, the etching method is preferably wet etching, and may be dry etching. (b) A thin-film material for the low acoustic impedance layer 152 is further deposited. The deposition method is preferably DC magnetron sputtering (or may be RF magnetron sputtering), and may be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. Then, the low acoustic impedance layer 152 is formed by coating (or spray coating), pre-baking, exposing, developing, post-baking, and etching the thin film of the low acoustic impedance layer 152. Here, wet etching is preferable as the etching technique, but dry etching may also be selected. Then, steps (a) and (b) are repeated until an acoustic mirror structure 15 satisfying the number of layers required by the design is obtained.

[0166] In step S63, the first electrode 11 is formed on the first base substrate 10 after the above steps are completed.

[0167] In some examples, step S63 may include depositing a first conductive thin film on the first base substrate 10. The deposition method is preferably DC magnetron sputtering (or RF magnetron sputtering), but may also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or the like, or may be a copper foil attachment method. The first conductive film may be coated (or spray coated), pre-baked, exposed, developed, and post-baked. Finally, etching is performed, preferably wet etching, or alternatively dry etching, to form a pattern including the first electrode 11.

[0168] In step S64, the induction layer 18 is formed on the first base substrate 10 after the above steps are completed.

[0169] In some examples, the material of the inductive layer 18 is preferably a graphene thin film, and may be a single layer, two layers, or multiple layers. For example, if the material of the first electrode 11 formed in step S63 is Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, or Au metal, or a Co-Ni or Au-Ni alloy, the inductive layer 18 may be graphene material. For example, the inductive layer 18 may be directly grown by magnetron sputtering chemical vapor deposition or microwave plasma chemical vapor deposition. Specifically, a mixture of methane, nitrogen, and argon gas is introduced, the substrate is heated to 600-800°C, and a reaction occurs to form a graphene thin film. If the first electrode 11 formed in step S63 is not one of the above metals or alloys, the inductive layer may be formed in two steps: (a) the first step is the formation of a graphene thin film. Metal foils, such as Fe, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, and Au metals, or Co-Ni and Au-Ni alloy foils, are placed in a reaction chamber and grown by magnetron sputtering or microwave plasma chemical vapor deposition. Specifically, a mixture of methane, nitrogen, and argon gas is introduced, and the substrate is heated to 600-800°C to form a graphene thin film. (b) The second step involves transferring the resulting graphene thin film from the metal foil to the first electrode 11. First, polymethyl methacrylate (PMMA) is sprayed or spin-coated onto the metal foil / graphene in an inert gas atmosphere, then dried and cured by heating at 120°C for 3-5 minutes. The metal foil / graphene / PMMA is then placed in the corresponding solution to dissolve the metal. For copper foil, a 20% FeCl3 solution is used. The remaining graphene / PMMA is floated on the surface of the solution, and the graphene / PMMA is removed and washed in deionized water. Then, the graphene / PMMA is transferred to the first electrode 11 and dried by irradiating it with an infrared lamp for 10 to 15 minutes. Finally, the PMMA is dissolved in an organic solvent, such as acetone, to complete the fabrication of the induction layer 18.

[0170] In step S65, the piezoelectric layer 12 is formed on the first base substrate 10 after the above steps are completed.

[0171] In some examples, for example, using hBN as the material for the piezoelectric layer 12, oriented growth of the piezoelectric material can be performed in step S65. RF magnetron sputtering is preferably used. The target is hBN. By controlling the Ar and N gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an oriented hBN thin film rich in nitrogen vacancies is formed (whose piezoelectric properties are superior to those of BN without nitrogen vacancies). The growth orientation is preferably (100), but may also be (001) or (111). The thin film deposition method may be pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), plasma-enhanced chemical vapor deposition (PECVD), or the like. The piezoelectric layer 12 is then subjected to photolithography, which includes coating (or spray coating), pre-baking, exposure, development, and post-baking. Finally, the piezoelectric material layer is etched to form a pattern of the piezoelectric layer 12 having the first connection vias 121, and the preferred etching technique may be a wet etching technique or a dry etching technique.

[0172] In step S66, the second electrodes 13 and the first connection electrodes 17 are formed on the first base substrate 10 after the above steps are completed.

[0173] In some examples, step S66 may include first depositing a second conductive thin film, preferably by DC magnetron sputtering (or RF magnetron sputtering), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, or electron beam evaporation. The second conductive thin film is sequentially coated (or spray coated), pre-baked, exposed, developed, and post-baked, and finally etched to form the second electrode 13 and the first connection electrode 17, preferably by wet etching or alternatively by dry etching. Because the second conductive thin film formed on the hole wall is thin and unfavorable for low-loss transmission of radio frequency signals, electroplating may be performed to thicken the second conductive thin film in the first connection via 121 before forming the second electrode 13 and the first connection pattern.

[0174] In step S67, a packaging layer 16 is formed on the first base substrate 10 after the above steps are completed.

[0175] In some examples, the material of the packaging layer 16 may be an organic material, polyimide. In this case, step S67 may include liquid coating of the organic material, which may be performed by spin coating, spraying, inkjet printing, transfer printing, or the like, followed by heat curing to form the pattern of the packaging layer 16.

[0176] An embodiment of the present disclosure further provides an electronic device that may include any of the bulk acoustic wave resonators described above.

[0177] It should be understood that the above-described embodiments are merely exemplary embodiments used to explain the principles of the present application, and the present application is not limited thereto. Those skilled in the art can make various modifications and improvements without departing from the spirit and substance of the present application, and these modifications and improvements are also considered to fall within the scope of the claims of the present application.

Claims

1. A bulk acoustic wave resonator comprising a first base substrate, a first electrode, a piezoelectric layer, and a second electrode, wherein the first electrode is provided on the first base substrate, the second electrode is provided on a side of the first electrode away from the first base substrate, the piezoelectric layer is provided between the first electrode and the second electrode, any two of the first electrode, the piezoelectric layer, and the second electrode at least partially overlap when orthogonally projected on the first base substrate, and the sound velocity of the material of the piezoelectric layer is 18,000 m / s or more.

2. 10. The bulk acoustic wave resonator of claim 1, wherein the material of the piezoelectric layer includes any one of hBN, cBN, and wBN.

3. 2. The bulk acoustic wave resonator of claim 1, further comprising a guide layer disposed between the first electrode and the piezoelectric layer, wherein a positive projection of the guide layer on the first base substrate covers a positive projection of the piezoelectric layer on the first base substrate.

4. The bulk acoustic wave resonator of claim 3 , wherein the material of the guiding layer comprises graphene.

5. 2. The bulk acoustic wave resonator of claim 1, further comprising a first connection electrode provided in the same layer as the second electrode, the first connection electrode being electrically connected to the first electrode through a first connection via that penetrates the piezoelectric layer.

6. 2. The bulk acoustic wave resonator of claim 1, wherein the material of the first electrode includes any one or more of Cu, Al, Mo, Co, Ag, Ti, Pt, Ru, W, and Au.

7. 7. The bulk acoustic wave resonator of claim 1, wherein the first base substrate has a first cavity penetrating through it in a thickness direction, the first base substrate includes a first surface and a second surface opposite to each other in the thickness direction, the first cavity includes a first opening and a second opening opposite to each other, the first opening is located on the first surface, the second opening is located on the second surface, and the first electrode covers the first opening.

8. 7. The bulk acoustic wave resonator according to claim 1, wherein the first base substrate has a first groove, the first base substrate includes a first surface and a second surface opposed to each other in a thickness direction thereof, the first groove includes a third opening located in the first surface, the first electrode is located in the first surface, and an outline of the third opening as orthogonally projected on the second surface is within an outline of the first electrode as orthogonally projected on the second surface.

9. 9. The bulk acoustic wave resonator of claim 8, wherein an isolation layer is provided between the first surface of the first base substrate and the first electrode.

10. 10. The bulk acoustic wave resonator according to claim 9, further comprising at least one first through hole penetrating the first electrode and the isolation layer, the first through hole communicating with the first groove portion.

11. 7. The bulk acoustic wave resonator of claim 1, further comprising at least one mirror structure layer provided between a first electrode and the first base substrate, the mirror structure including a first sub-structure layer and a second sub-structure layer sequentially provided in a direction away from the first base substrate, and the acoustic impedance of the material of the first sub-structure layer being greater than the acoustic impedance of the material of the second sub-structure layer.

12. 7. The bulk acoustic wave resonator according to claim 1, further comprising a packaging layer provided on a side of the second electrode away from the first base substrate, the packaging layer covering the first electrode, the piezoelectric layer and the second electrode.

13. A method for manufacturing a bulk acoustic wave resonator, comprising sequentially forming a first electrode, a piezoelectric layer, and a second electrode on a first base substrate, wherein orthogonal projections of any two of the first electrode, the piezoelectric layer, and the second electrode on the first base substrate at least partially overlap, and the sound velocity of the material of the piezoelectric layer is 18,000 m / s or more.

14. 14. The method for manufacturing a bulk acoustic wave resonator according to claim 13, wherein the material of the piezoelectric layer includes any one of hBN, cBN, and wBN.

15. 14. The method of claim 13, wherein forming the piezoelectric layer includes forming the piezoelectric layer using RF magnetron sputtering.

16. 16. The method of claim 15, further comprising forming a dielectric layer before forming the first electrode and the piezoelectric layer.

17. 16. The method for manufacturing a bulk acoustic wave resonator according to claim 15, wherein a first connection electrode is further formed simultaneously with forming the second electrode, and the manufacturing method further includes forming a first connection via that penetrates the piezoelectric layer in a thickness direction thereof, and the first connection electrode is connected to the first electrode through the first connection via.

18. 18. The method for manufacturing a bulk acoustic wave resonator according to claim 13, further comprising: processing the first base substrate to include a first cavity penetrating the first base substrate in a thickness direction, the first base substrate including a first surface and a second surface opposite to each other in the thickness direction, the first cavity including a first opening and a second opening opposite to each other, the first opening being located in the first surface, the second opening being located in the second surface, and the first electrode covering the first opening.

19. 18. The method for manufacturing a bulk acoustic wave resonator according to claim 13, further comprising: processing the first base substrate to have a first groove, the first base substrate including a first surface and a second surface opposed to each other in a thickness direction thereof, the first groove including a third opening, the third opening being located on the first surface, the first electrode being located on the first surface, and an outline of the third opening as orthogonally projected on the second surface being located within an outline of the first electrode as orthogonally projected on the second surface.

20. forming a filling structure in the first trench; forming an isolation layer on a side of the first groove portion away from the first base substrate, and forming the first electrode on the isolation layer on a side of the first groove portion away from the first base substrate; 20. The method for manufacturing a bulk acoustic wave resonator according to claim 19, further comprising: forming a first through-hole penetrating the first electrode and the isolation layer; and etching away the filling structure through the first through-hole.

21. Before forming the first electrode, 18. A method for manufacturing a bulk acoustic wave resonator according to claim 13, comprising: forming at least one mirror structure layer on the first base substrate; and forming a mirror structure including a first sub-structure layer and a second sub-structure layer formed sequentially in a direction away from the first base substrate, wherein the acoustic impedance of a material of the first sub-structure layer is greater than the acoustic impedance of a material of the second sub-structure layer.

22. 18. The method for manufacturing a bulk acoustic wave resonator according to claim 13, further comprising forming a packaging layer on a side of the second electrode away from the first base substrate, the packaging layer covering the first electrode, the piezoelectric layer, and the second electrode.

23. An electronic device comprising the bulk acoustic wave resonator according to any one of claims 1 to 12.

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