Bulk acoustic wave resonator, preparation method thereof and electronic equipment

Abstract

The invention provides a bulk acoustic wave resonator, a preparation method thereof and electronic equipment, and belongs to the technical field of communication. The bulk acoustic wave resonator comprises a substrate (10), a first electrode (11), a piezoelectric layer (12) and a second electrode (13), the bulk acoustic wave resonator further comprises a first bias resistance layer (17) arranged on the side, close to the substrate (10), of the first electrode (11), and a first electrical isolation layer (18) arranged between the first bias resistance layer (17) and the first electrode (11). The first bias resistance layer (17) is made of a high-resistivity material; and / or, a second bias resistive layer (110) disposed on one side of the second electrode (13) facing away from the substrate (10), and a second electrical isolation layer (19) disposed between the second bias resistive layer (110) and the second electrode (13); and the second bias resistance layer (110) is made of a high-resistivity material.

Description

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

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

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

[0003] BAW resonators, the basic structural unit of BAW filters, currently use a silicon wafer as the substrate material. A sandwich structure is formed from the bottom up, with a first electrode, a piezoelectric layer, and a second electrode. The first and second electrodes are metal electrodes, while the piezoelectric layer is made of piezoelectric material.

[0004] The working principle of a bulk acoustic wave resonator is as follows: an RF signal is transmitted from the electrode at one end of the resonator and then converted into a mechanical vibration acoustic wave signal through the inverse piezoelectric effect at the interface between the piezoelectric material and the metal electrode. This acoustic wave signal forms a resonant standing wave with a certain frequency in the sandwich structure of the first electrode, the piezoelectric layer, and the second electrode. The frequency of the RF signal is equal to the resonant frequency of the resonator. The acoustic wave signal is transmitted to the electrode at the other end of the resonator and is converted into an RF signal through the piezoelectric effect at the interface between the metal electrode and the piezoelectric material. The resonator has a fixed resonant frequency. When the frequency of the RF signal is equal to the resonant frequency of the resonator, the conversion efficiency of RF signal → acoustic wave signal → RF signal is high. When the frequency of the RF signal is not equal to the resonant frequency of the resonator, the conversion efficiency of RF signal → acoustic wave signal → RF signal is very low, and most RF signals cannot be transmitted from the resonator. In other words, the resonator functions as a filter, filtering the RF signal. In order to reduce the insertion loss during the filtering process, the acoustic wave signal needs to be confined as much as possible inside the piezoelectric material to prevent the acoustic wave signal from spreading outward. Therefore, acoustic wave reflectors are usually constructed on the upper and lower surfaces of the resonator.

[0005] Summary of the Invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art and provides a bulk acoustic wave resonator, a preparation method thereof, and an electronic device.

[0007] An embodiment of the present disclosure provides a bulk acoustic wave resonator, comprising: a substrate, a first electrode, a piezoelectric layer, and a second electrode; the first electrode is disposed on the substrate, the second electrode is disposed on a side of the first electrode facing away from the substrate, the piezoelectric layer is disposed between the first electrode and the second electrode, and the orthographic projections of any two of the first electrode, the piezoelectric layer, and the second electrode on the substrate at least partially overlap; wherein the bulk acoustic wave filter further comprises:

[0008] a first bias resistor layer provided on a side of the first electrode close to the substrate, and a first electrical isolation layer provided between the first bias resistor layer and the first electrode; the first bias resistor layer is made of a high resistivity material; and / or,

[0009] A second bias resistor layer is provided on the side of the second electrode away from the base substrate, and a second electrical isolation layer is provided between the second bias resistor layer and the second electrode; the second bias resistor layer is made of a high resistivity material.

[0010] The base substrate has a first cavity penetrating along its thickness direction.

[0011] Wherein, it further includes at least one reflector structure provided on a side of the base substrate close to the first electrode; when the base substrate is provided with the first bias resistor layer, the reflector structure is provided on a side of the first bias resistor layer close to the base substrate;

[0012] The reflector structure includes a first substructure layer and a second substructure layer sequentially arranged in a direction away from the substrate, and the acoustic impedance of the material of the first substructure layer is greater than the acoustic impedance of the material of the second substructure layer.

[0013] When the bulk acoustic wave resonator includes the first bias resistor layer, the material of the first bias resistor layer includes a single-layer structure of any one of ITO, IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, Constantan alloy, manganese-copper alloy, nickel-chromium alloy, and iron-chromium-aluminum alloy, or a stacked-layer structure of multiple materials.

[0014] When the bulk acoustic wave resonator includes the second bias resistor layer, the second bias resistor layer includes a single-layer structure of any one of ITO, IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese-copper alloy, nickel-chromium alloy, and iron-chromium-aluminum alloy, or a stacked-layer structure of multiple materials.

[0015] When the BAW resonator includes the first electrical isolation layer, the material of the first electrical isolation layer includes a single-layer structure of any one of Si3N4, SiO2, Al2O3, AlN, and BN, or a stacked-layer structure of multiple materials.

[0016] When the BAW resonator includes the second electrical isolation layer, the material of the second electrical isolation layer includes a single-layer structure of any one of Si3N4, SiO2, Al2O3, AlN, and BN, or a stacked-layer structure of multiple materials.

[0017] The substrate may be made of any one of glass, Si, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, and GaO.

[0018] The piezoelectric materials include AlN, doped AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF; wherein the doped AlN includes Al (1-x) Sc x N, Al (1-x) Cr x N, Al (1-x) Y x N, Al (1-x) Ti x N, Al (1-x) Zr x N, Al (1-x) Hf x N, Al (1-x) Yb x N, Al (1-x) Ta x N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al(1-x) N, Zn 0.25 Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 Any one of N.

[0019] Wherein, the first electrode and the second electrode both include any one of Mo, Al, Cu, Co, Ag, Ti, Pt, Ru, W, and Au.

[0020] An embodiment of the present disclosure provides a method for preparing a bulk acoustic wave resonator, comprising: forming a first electrode, a piezoelectric layer, and a second electrode in sequence on a first substrate, wherein the orthographic projections of any two of the first electrode, the piezoelectric layer, and the second electrode on the first substrate at least partially overlap; wherein:

[0021] The preparation method further includes: forming a first bias resistor layer on a side of the first electrode close to the substrate, and forming a first electrical isolation layer between the first bias resistor layer and the first electrode; the material of the first bias resistor layer is a high resistivity material; and / or,

[0022] A second bias resistor layer is formed on the side of the second electrode facing away from the base substrate, and a second electrical isolation layer is formed between the second bias resistor layer and the second electrode; the second bias resistor layer is made of a high resistivity material.

[0023] The method for preparing the bulk acoustic wave resonator further comprises:

[0024] The base substrate is processed to form a first cavity penetrating along a thickness direction of the base substrate.

[0025] Wherein, at least one reflector structure is formed on a side of the base substrate close to the first electrode; when the first bias resistor layer is formed on the base substrate, the reflector structure is formed on a side of the first bias resistor layer close to the base substrate;

[0026] Forming the reflector structure includes sequentially forming a first substructure layer and a second substructure layer in a direction away from the substrate, and the acoustic impedance of the material of the first substructure layer is greater than the acoustic impedance of the material of the second substructure layer.

[0027] When the bulk acoustic wave resonator includes the first bias resistor layer, the material of the first bias resistor layer includes a single-layer structure of any one of ITO, IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, Constantan alloy, manganese-copper alloy, nickel-chromium alloy, and iron-chromium-aluminum alloy, or a stacked-layer structure of multiple materials.

[0028] When the bulk acoustic wave resonator includes the second bias resistor layer, the second bias resistor layer includes a single-layer structure of any one of ITO, IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese-copper alloy, nickel-chromium alloy, and iron-chromium-aluminum alloy, or a stacked-layer structure of multiple materials.

[0029] When the BAW resonator includes the first electrical isolation layer, the material of the first electrical isolation layer includes a single-layer structure of any one of Si3N4, SiO2, Al2O3, AlN, and BN, or a stacked-layer structure of multiple materials.

[0030] When the BAW resonator includes the second electrical isolation layer, the material of the second electrical isolation layer includes a single-layer structure of any one of Si3N4, SiO2, Al2O3, AlN, and BN, or a stacked-layer structure of multiple materials.

[0031] The substrate may be made of any one of glass, Si, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, and GaO.

[0032] The piezoelectric materials include AlN, doped AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF; wherein the doped AlN includes Al (1-x) Sc x N, Al (1-x) Cr x N, Al (1-x) Y x N, Al (1-x) Ti x N, Al (1-x) Zr x N, Al (1-x) Hf x N, Al(1-x) Yb x N, Al (1-x) Ta x N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al (1-x) N, Zn 0.25 Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 Any one of N.

[0033] Wherein, the first electrode and the second electrode both include any one of Mo, Al, Cu, Co, Ag, Ti, Pt, Ru, W, and Au.

[0034] An embodiment of the present disclosure provides an electronic device, comprising any of the above-mentioned bulk acoustic wave resonators. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a schematic structural diagram of a back-etched bulk acoustic wave resonator.

[0036] FIG2 is a schematic structural diagram of a thin film bulk acoustic wave resonator.

[0037] FIG3 is a schematic structural diagram of another thin film bulk acoustic wave resonator.

[0038] FIG4 is a schematic structural diagram of a solid-state assembled bulk acoustic wave resonator.

[0039] FIG5 is a schematic structural diagram of a first exemplary BAW resonator implemented in the present disclosure.

[0040] FIG6 is a flow chart of the preparation process of the BAW resonator shown in FIG5 .

[0041] FIG7 is a schematic structural diagram of a second exemplary BAW resonator implemented in the present disclosure.

[0042] FIG8 is a flow chart of the preparation process of the BAW resonator shown in FIG7 .

[0043] FIG9 is a schematic structural diagram of a third exemplary BAW resonator implemented in the present disclosure.

[0044] FIG10 is a flow chart of the preparation process of the BAW resonator shown in FIG9 .

[0045] FIG11 is a schematic structural diagram of a fourth example of a bulk acoustic wave resonator implemented in the present disclosure.

[0046] FIG. 12 is a flow chart of the preparation process of the BAW resonator shown in FIG. 11 .

[0047] FIG13 is a schematic structural diagram of a fifth exemplary BAW resonator implemented in the present disclosure.

[0048] FIG. 14 is a flow chart of the preparation process of the BAW resonator shown in FIG. 13 .

[0049] FIG15 is a schematic structural diagram of a sixth exemplary BAW resonator implemented in the present disclosure.

[0050] FIG. 16 is a flow chart of the preparation process of the BAW resonator shown in FIG. 15 . DETAILED DESCRIPTION

[0051] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0052] Unless otherwise defined, the technical or scientific terms used in this disclosure should have the usual meanings understood by people with ordinary skills in the field to which this disclosure belongs. The words "first", "second" and similar words used in this disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. Similarly, words such as "one", "an" or "the" do not indicate a quantity limitation, but rather indicate the existence of at least one. Words such as "include" or "comprise" mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Words such as "connect" or "connected" are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the object being described changes, the relative positional relationship may also change accordingly.

[0053] As shown in Figures 1-4, to reduce insertion loss during filtering, a bulk acoustic wave resonator (BAW) needs to confine the acoustic wave signal as much as possible within the piezoelectric layer 12 between the first and second electrodes 13 to prevent the acoustic wave signal from spreading outward. Therefore, acoustic wave reflectors are usually constructed on the upper and lower surfaces of the resonator. The upper surface generally uses a low-acoustic-impedance air medium as a reflector. Depending on the construction of the acoustic wave reflector on the lower surface, BAW resonators are divided into three major categories: back-etched BAW resonators, as shown in Figure 1; film bulk acoustic resonators (FBARs), as shown in Figures 2 and 3; and solid mounted resonators (SMRs), as shown in Figure 4. In the FBAR, a first groove 102 is constructed below the first electrode, etched into the substrate 10, to serve as an air gap. The first electrode is then supported by an isolation layer 14, as shown in Figure 2. Alternatively, a first groove 102 is formed through an isolation layer 14 as an air gap, as shown in FIG3 . In the SMR method, an acoustic reflector structure 15 is constructed below the first electrode, which is formed by alternating and repeating high acoustic impedance layers 151 and low acoustic impedance material layers 152 . In the back-etch type, a first cavity 101 is formed on the substrate 10 below the first electrode to serve as an air layer by deeply etching the back side of the silicon substrate to form a cavity.

[0054] The inventors discovered that the piezoelectric material of the piezoelectric layer in current bulk acoustic wave filters is C-axis oriented crystallized AlN and Sc-doped AlN. As the temperature rises, the in-plane lattice constant increases and the out-of-plane lattice constant decreases, resulting in a decrease in the speed of sound wave propagation. According to the qualitative formula: f = v / (2h), where f is the resonant frequency, v is the speed of sound wave propagation in the thickness direction of the piezoelectric material, and h is the thickness of the piezoelectric material, it can be obtained that the resonant frequency decreases, that is, a temperature drift phenomenon (negative temperature coefficient, typically -30ppm) occurs, which is harmful to the performance of the communication system. To solve this problem, a thin film with a positive temperature coefficient is usually added near the piezoelectric layer. The main materials are SiO2 and SiO2 doped with F or P. However, because it is inherently insulating and non-conductive, it will hinder the piezoelectric effect and the inverse piezoelectric effect near the piezoelectric layer, reducing the effective electromechanical coupling coefficient of the resonator, resulting in a decrease in the quality factor of the device and deterioration of performance.

[0055] In response to the above technical problems, a bulk acoustic wave resonator is provided in an embodiment of the present disclosure. By applying a DC electric field to the piezoelectric layer, the acoustic wave propagation velocity of the piezoelectric layer material is modulated and changed, thereby changing the resonant frequency of the bulk acoustic wave resonator. When the resonant frequency of the bulk acoustic wave resonator drifts toward the low frequency direction due to the increase in temperature (i.e., temperature drift occurs), a suitable DC bias is applied to both sides of the piezoelectric layer of the bulk acoustic wave resonator to generate a stable DC electric field that penetrates the piezoelectric layer, which will cause the resonant frequency of the bulk acoustic wave resonator to drift toward the high frequency direction (i.e., electric field drift occurs), and the final result is that the frequency of the bulk acoustic wave resonator remains unchanged. Conversely, when the temperature decreases, the DC bias is appropriately adjusted in the opposite direction to keep the frequency of the bulk acoustic wave resonator unchanged.

[0056] The following describes in detail a bulk acoustic wave resonator and a preparation method thereof according to an embodiment of the present disclosure with reference to specific examples.

[0057] First Example: Figure 5 is a schematic structural diagram of a BAW resonator according to the first example of the embodiment of the present disclosure. As shown in Figure 5, the BAW resonator includes a substrate 10, and a first electrode 11, a piezoelectric layer 12, and a second electrode 13 sequentially disposed on the substrate 10. The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the substrate 10 at least partially overlap. The substrate 10 has a first cavity 101 extending through its thickness. In this case, after an RF signal is transmitted into the BAW resonator, it is converted into an acoustic wave signal through the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12. The acoustic wave signal propagates longitudinally in the piezoelectric layer 12, and upon reaching the interface between the first electrode 11 and the piezoelectric layer 12, it is converted back into an RF signal through the piezoelectric effect, and finally transmitted out of the resonator. The first cavity 101 below the BAW resonator and the air layer above it act as acoustic reflectors, confining the acoustic signal within the resonator structure rather than dissipating it, thereby reducing the loss of the BAW resonator.

[0058] When performing real-time frequency compensation, a DC bias is applied between the first electrode 11 and the second electrode 13 to generate a DC electric field in the piezoelectric layer 12. When the direction of the DC electric field is from the first electrode 11 to the second electrode 13, the electric field strength increases from 0 to +100 V / um as the DC bias increases, and the resonant frequency of the bulk acoustic wave resonator moves toward a low frequency; when the direction of the DC electric field is from the second electrode 13 to the first electrode 11, the electric field strength increases from 0 to -100 V / um as the DC bias increases, and the resonant frequency of the bulk acoustic wave resonator moves toward a high frequency. Under the action of DC electric field modulation (in order to prevent the DC signal from mixing into the RF signal and breaking down the RF circuit, a DC block needs to be added to the RF circuit outside the BAW resonator), the resonant frequency of the BAW resonator is controlled to move linearly, and the movement range is 28 to 58 ppm·f0 / (V / um). For the doped AlN piezoelectric material, the movement range is greater than that of the piezoelectric layer 12 material of the undoped AlN, where f0 is the initial resonant frequency when no DC bias is applied, and V / um is the electric field strength applied to the piezoelectric layer 12. The specific usage scenario is that when the ambient temperature changes, the resonant frequency of the BAW resonator will drift with temperature (shifting to low frequency when the temperature rises and shifting to high frequency when the temperature drops), which in turn causes the filtering curve of the filter to drift with temperature. At this time, by adjusting the DC bias applied to the piezoelectric layer 12, the resonant frequency of the BAW resonator moves in the opposite direction of the temperature drift, achieving the final effect of unchanged resonant frequency, thereby ensuring that the filtering curve of the filter remains unchanged when the ambient temperature changes.

[0059] In some examples, an encapsulation layer 16 is further provided on a side of the second electrode 13 facing away from the base substrate 10 to isolate water vapor and oxygen to prevent device damage.

[0060] Furthermore, the material of the encapsulation layer 16 is preferably an organic compound that can isolate water vapor and oxygen, such as polyimide, epoxy resin, etc., or an inorganic material such as SiN x , Al2O3, etc. The encapsulation layer 16 can be a single layer of a single material, or a stacked configuration of multiple materials.

[0061] In some examples, the material of the base substrate 10 is preferably glass, and Si, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, GaO and other materials can also be selected. The thickness of the base substrate 10 ranges from 0.1um to 10mm.

[0062] In some examples, the material of the first electrode 11 is preferably molybdenum (Mo), as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the material of the piezoelectric layer 12. The material of the first electrode 11 can also be Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au, or a stack or alloy of these metals. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0063] In some examples, the material of the piezoelectric layer 12 is preferably AlN and doped AlN, such as Al (1-x) Sc x N, Al (1-x) Cr x N, Al (1-x) Y x N, Al (1-x) Ti x N, Al (1-x) Zr x N, Al (1-x) Hf x N, Al (1-x) Yb x N, Al (1-x) Ta x N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al (1-x) N, Zn 0.25 Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 N. The material of the piezoelectric layer 12 can also be selected from ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. The material of the piezoelectric layer 12 can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0064] In some examples, the material of the second electrode 13 is preferably molybdenum (Mo), as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au may also be selected as the material of the second electrode 13. The material of the second electrode 13 may also be a stack or alloy of the aforementioned metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0065] Next, a first example of a method for preparing a BAW resonator is described. As shown in FIG6 , the method specifically includes the following steps.

[0066] S11 , providing a base substrate 10 .

[0067] Taking the substrate 10 as an example of a single crystal silicon substrate, step S11 can specifically include: first, ultrasonically clean the single crystal silicon substrate with deionized water; then place it in a mixed solution of H2SO4:H2O=3:1, heat it to 250°C and wash it for 15 minutes; then place it in deionized water and ultrasonically clean it; then place it in a mixed solution of NH4OH:H2O=1:6, heat it to 80°C and wash it for 15 minutes; take it out and place it in deionized water for rinsing; next, place it in a mixed solution of HCl:H2O2:H2O=1:1:5, heat it to 85°C and wash it for 15 minutes, take it out and place it in dilute hydrofluoric acid of HF:H2O=1:20 and rinse it for 10 seconds to remove the surface oxide layer; finally, place it in deionized water for ultrasonic cleaning for 20 minutes, blow it dry with an air knife, and complete the entire cleaning process of the substrate 10.

[0068] S12 , forming a first electrode 11 on the base substrate 10 .

[0069] When the first electrode 11 is made of a metal material, step S12 may include depositing a first metal film on the base substrate 10. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Alternatively, a copper foil attachment method can be used. The first metal film is then subjected to a photolithography process, including glue coating (or glue spraying), pre-baking, exposure, development, and post-baking. Next, etching is performed to form a pattern including the first electrode 11. The etching process preferably adopts a wet etching process, and a dry etching process can also be selected. Finally, a de-gumming process is performed to complete the preparation of the first electrode.

[0070] S13 , forming a piezoelectric layer 12 on a side of the first electrode 11 facing away from the substrate 10 .

[0071] Taking the piezoelectric layer 12 as an example of an AlN single-layer structure, step S13 may include forming a piezoelectric material layer on the side of the first electrode 11 away from the substrate 10, and performing oriented growth of the piezoelectric material layer. The piezoelectric material layer is preferably formed by radio frequency magnetron sputtering (DC measurement and control sputtering is also acceptable). For AlN piezoelectric material, the target material is Al. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an AlN C-axis oriented piezoelectric material layer is formed, and the preferred growth orientation is (001). The deposition method of the piezoelectric material layer can also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. Next, the piezoelectric layer 12 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Etching is then performed to form a pattern including the piezoelectric layer 12. A wet etching process is preferred, but a dry etching process can also be selected. Finally, a debonding process is performed to complete the preparation of the piezoelectric layer 12 .

[0072] S14 . Form a second electrode 13 on a side of the piezoelectric layer 12 facing away from the first electrode 11 .

[0073] When the second electrode 13 is made of a metal material, step S14 may specifically include first depositing a second metal film on the side of the piezoelectric layer 12 away from the first electrode 11. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Next, the second metal film is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Thereafter, etching is performed to form a pattern including the second electrode 13. The etching process is preferably a wet etching process, and a dry etching process can also be selected. Finally, a de-bonding process is performed to complete the preparation of the second electrode 13.

[0074] S15 , forming an encapsulation layer 16 on a side of the second electrode 13 facing away from the base substrate 10 .

[0075] Taking the encapsulation layer 16 as an example, the step S15 may specifically include first coating the organic material liquid, which may be done by spin coating, spraying, inkjet printing, transfer printing, etc., and then heating and curing to form a pattern of the encapsulation layer 16.

[0076] S16 , turning over the base substrate 10 forming the above structure, and etching to form a first cavity 101 penetrating along the thickness direction of the base substrate 10 .

[0077] In some examples, step S16 may include flipping the base substrate 10 formed with the above structure, preparing a mask pattern on the back of the base substrate 10, and performing a photolithography process including resist coating (or spraying), pre-baking, exposure, development, and post-baking. HF acid wet etching is then performed to form the first cavity 101, and finally a resist stripping process is performed.

[0078] Second example: FIG7 is a schematic structural diagram of a bulk acoustic wave resonator of the second example of an embodiment of the present disclosure; as shown in FIG7 , the bulk acoustic wave resonator includes a substrate 10, and a first bias resistor layer 17, a first electrical isolation layer 18, a first electrode 11, a piezoelectric layer 12, and a second electrode 13 sequentially arranged on the substrate 10. The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the substrate 10 at least partially overlap. The substrate 10 has a first cavity 101 that runs through it along its thickness direction. In this case, after the radio frequency signal is transmitted into the bulk acoustic wave resonator, it is converted into an acoustic wave signal through the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, propagates longitudinally in the piezoelectric layer 12, and is converted into a radio frequency signal through the piezoelectric effect when it reaches the interface between the first electrode 11 and the piezoelectric layer 12, and finally transmitted out of the resonator. The first cavity 101 below the BAW resonator and the air layer above it act as acoustic reflectors, which confine the acoustic signal in the resonator structure rather than dissipating it, thereby reducing the loss of the BAW resonator.

[0079] During real-time frequency compensation, a DC bias is applied between the first bias resistor layer 17 and the second electrode 13, generating a DC electric field in the piezoelectric layer 12. When the DC electric field is directed from the first bias resistor layer 17 to the second electrode 13, the electric field strength increases from 0 to +100 V / um as the DC bias increases, shifting the resonant frequency of the BAW resonator toward lower frequencies. When the DC electric field is directed from the second electrode 13 to the first bias resistor layer 17, the electric field strength increases from 0 to -100 V / um as the DC bias increases, shifting the resonant frequency of the BAW resonator toward higher frequencies. Under DC electric field modulation (to prevent DC signals from mixing into RF signals and disrupting the RF circuit, a DC block is required in the RF circuit outside the BAW resonator chip), the resonant frequency of the BAW resonator is controlled to shift linearly within a range of 28 to 58 ppm·f0 / (V / um). For doped AlN piezoelectric materials, this range is greater than for undoped AlN piezoelectric materials. Where f0 is the initial resonant frequency when no DC bias is applied, and V / um is the electric field strength applied to the piezoelectric layer 12. Specifically, when the ambient temperature changes, the resonant frequency of the BAW resonator will drift with temperature (shifting toward lower frequencies when the temperature rises and toward higher frequencies when the temperature drops), which in turn causes the filter's filtering curve to drift with temperature. At this time, by adjusting the DC bias applied to the piezoelectric layer 12, the resonant frequency of the BAW resonator shifts in the opposite direction of the temperature drift, achieving the ultimate effect of a constant resonant frequency, thus ensuring that the filter's filtering curve remains unchanged when the ambient temperature changes.

[0080] Compared with the first example, in the second example, a first bias resistor layer 17 and a first electrical isolation layer 18 are added between the first electrode 11 and the base substrate 10 to isolate the DC signal and the RF signal in the lower half of the BAW resonator.

[0081] In some examples, an encapsulation layer 16 is further provided on a side of the second electrode 13 facing away from the base substrate 10 to isolate water vapor and oxygen to prevent device damage.

[0082] Furthermore, the material of the encapsulation layer 16 is preferably an organic compound that can isolate water vapor and oxygen, such as polyimide, epoxy resin, etc., or an inorganic material such as SiN x , Al2O3, etc. The encapsulation layer 16 can be a single layer of a single material, or a stacked configuration of multiple materials.

[0083] In some examples, the material of the base substrate 10 is preferably glass, and Si, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, GaO and other materials can also be selected. The thickness of the base substrate 10 ranges from 0.1um to 10mm.

[0084] In some examples, the material of the first bias resistor layer 17 is a conductive material with high resistivity, preferably ITO, but may also include IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese copper alloy, nickel-chromium alloy, iron-chromium-aluminum alloy, and the like. The material may be a single material or a stack of the above materials. The thickness of the first bias resistor layer 17 ranges from 1 nm to 10 μm.

[0085] In some embodiments, the first electrical isolation layer 18 is made of an insulating material, preferably Si3N4, but can also be made of SiO2, Al2O3, AlN, BN, etc. It can be a single material or a stack of the above materials. The thickness of the electrical isolation layer ranges from 1 nm to 10 μm.

[0086] In some examples, the material of the first electrode 11 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. The material of the first electrode 11 may also be Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au, or a stack or alloy of these metals. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0087] In some examples, the material of the piezoelectric layer 12 is preferably AlN and doped AlN, such as Al (1-x) Sc x N, Al (1-x) Cr x N, Al (1-x) Y x N, Al (1-x) Ti x N, Al (1-x) Zr x N, Al (1-x) Hf x N, Al (1-x) Yb x N, Al (1-x) Ta x N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al (1-x) N, Zn 0.25Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 N. The material of the piezoelectric layer 12 can also be selected from ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. The material of the piezoelectric layer 12 can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0088] In some examples, the material of the second electrode 13 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au may also be selected as the material of the second electrode 13. The material of the second electrode 13 may also be a stack or alloy of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0089] Next, a second example of a method for preparing a BAW resonator is described. As shown in FIG8 , the method specifically includes the following steps.

[0090] S21 , providing a base substrate 10 .

[0091] Taking the substrate 10 as an example of a single crystal silicon substrate, step S21 can specifically include: first, ultrasonically clean the single crystal silicon substrate with deionized water; then place it in a mixed solution of H2SO4:H2O=3:1, heat it to 250°C and wash it for 15 minutes; then place it in deionized water for ultrasonic cleaning; then place it in a mixed solution of NH4OH:H2O=1:6, heat it to 80°C and wash it for 15 minutes; take it out and place it in deionized water for rinsing; next, place it in a mixed solution of HCl:H2O2:H2O=1:1:5, heat it to 85°C and wash it for 15 minutes, take it out and place it in dilute hydrofluoric acid of HF:H2O=1:20 and rinse it for 10 seconds to remove the surface oxide layer; finally, place it in deionized water for ultrasonic cleaning for 20 minutes, blow it dry with an air knife, and complete the entire substrate 10 cleaning process.

[0092] S22 , forming a first bias resistor layer 17 on the base substrate 10 .

[0093] Specifically, step S22 can first deposit a high-resistivity conductive material film. The deposition method is preferably radio frequency magnetron sputtering (DC magnetron sputtering is also acceptable). Alternatively, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can be selected. Alternatively, a metal foil or alloy foil can be attached. The conductive material film undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, or a dry etching process can be selected to complete the preparation of the first bias resistor layer 17.

[0094] S23 , forming a first electrical isolation layer 18 on a side of the first bias resistor layer 17 facing away from the base substrate 10 .

[0095] Specifically, step S23 may include first depositing an electrically insulating material, and the deposition method may be radio frequency controlled sputtering, pulsed laser sputtering (PLD), atomic layer deposition (ALD), or plasma chemical vapor deposition (PECVD). The electrically insulating material undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, but a dry etching process may also be selected to complete the preparation of the first electrically insulating layer 18.

[0096] S24 , forming a first electrode 11 on a side of the base substrate 10 facing away from the first electrical isolation layer 18 .

[0097] When the first electrode 11 is made of a metal material, step S24 may include depositing a first metal film on the base substrate 10. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable). Alternatively, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. may be selected. Alternatively, a copper foil attachment method may be used. The first metal film is then subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Next, etching is performed to form a pattern including the first electrode 11. The etching process preferably uses a wet etching process, but a dry etching process may also be selected. Finally, a de-bonding process is performed to complete the preparation of the first electrode.

[0098] S25 , forming a piezoelectric layer 12 on a side of the first electrode 11 facing away from the substrate 10 .

[0099] Taking the piezoelectric layer 12 as an example of an AlN single-layer structure, step S25 may include forming a piezoelectric material layer on the side of the first electrode 11 away from the substrate 10, and performing oriented growth of the piezoelectric material layer. The piezoelectric material layer is preferably formed by radio frequency magnetron sputtering (DC measurement and control sputtering is also acceptable). For AlN piezoelectric material, the target material is Al. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an AlN C-axis oriented piezoelectric material layer is formed, and the preferred growth orientation is (001). The deposition method of the piezoelectric material layer can also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. Next, the piezoelectric layer 12 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Etching is then performed to form a pattern including the piezoelectric layer 12. A wet etching process is preferably used, but a dry etching process can also be used. Finally, a debonding process is performed to complete the preparation of the piezoelectric layer 12 .

[0100] S26 . Form a second electrode 13 on a side of the piezoelectric layer 12 facing away from the first electrode 11 .

[0101] When the second electrode 13 is made of a metal material, step S26 may specifically include first depositing a second metal film on the side of the piezoelectric layer 12 away from the first electrode 11. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Next, the second metal film is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Thereafter, etching is performed to form a pattern including the second electrode 13. The etching process is preferably a wet etching process, and a dry etching process can also be selected. Finally, a de-bonding process is performed to complete the preparation of the second electrode 13.

[0102] S27 , forming an encapsulation layer 16 on a side of the second electrode 13 facing away from the base substrate 10 .

[0103] Taking the encapsulation layer 16 as an example, the step S27 may specifically include first coating the organic material liquid, which may be done by spin coating, spraying, inkjet printing, transfer printing, etc., and then heating and curing to form a pattern of the encapsulation layer 16.

[0104] S28 , turning over the base substrate 10 forming the above structure, and etching to form a first cavity 101 penetrating along the thickness direction of the base substrate 10 .

[0105] In some examples, step S28 may include flipping the base substrate 10 having the above structure, preparing a mask pattern on the back of the base substrate 10, performing a photolithography process including resist coating (or spraying), pre-baking, exposure, development, and post-baking. HF acid wet etching is then performed to form the first cavity 101, followed by a resist stripping process.

[0106] Third example: FIG9 is a schematic structural diagram of a bulk acoustic wave resonator of the third example of an embodiment of the present disclosure; as shown in FIG9 , the bulk acoustic wave resonator includes a substrate 10, and a first bias resistor layer 17, a first electrical isolation layer 18, a first electrode 11, a piezoelectric layer 12, a second electrode 13, a second electrical isolation layer 19, and a second bias resistor layer 110 sequentially arranged on the substrate 10. The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the substrate 10 at least partially overlap. The substrate 10 has a first cavity 101 that runs through it along its thickness direction. In this case, after the radio frequency signal is transmitted into the bulk acoustic wave resonator, it is converted into an acoustic wave signal by the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12, propagates longitudinally in the piezoelectric layer 12, and is converted into a radio frequency signal by the piezoelectric effect when it reaches the interface between the first electrode 11 and the piezoelectric layer 12, and finally transmits out of the resonator. The first cavity 101 below the BAW resonator and the air layer above it act as acoustic reflectors, which confine the acoustic signal in the resonator structure rather than dissipating it, thereby reducing the loss of the BAW resonator.

[0107] During real-time frequency compensation, a DC bias is applied between the first bias resistor layer 17 and the second bias resistor layer 110, generating a DC electric field in the piezoelectric layer 12. When the DC electric field is directed from the first bias resistor layer 17 to the second bias resistor layer 110, the electric field strength increases from 0 to +100 V / μm as the DC bias increases, shifting the resonant frequency of the BAW resonator toward lower frequencies. When the DC electric field is directed from the second bias resistor layer 110 to the first bias resistor layer 17, the electric field strength increases from 0 to -100 V / μm as the DC bias increases, shifting the resonant frequency of the BAW resonator toward higher frequencies. Under DC field modulation, the resonant frequency of the BAW resonator is controlled to shift linearly within a range of 28 to 58 ppm·f0 / (V / μm). For doped AlN piezoelectric materials, the shift range is greater than for undoped AlN piezoelectric materials. Here, f0 is the initial resonant frequency without a DC bias, and V / μm is the electric field strength applied to the piezoelectric layer 12. The specific usage scenario is that when the ambient temperature changes, the resonant frequency of the bulk acoustic wave resonator will drift with temperature (shift to low frequency when the temperature rises, and shift to high frequency when the temperature drops), which in turn causes the filtering curve of the filter to drift with temperature. At this time, by adjusting the DC bias applied to the piezoelectric layer 12, the resonant frequency of the bulk acoustic wave resonator moves in the opposite direction of the temperature drift, achieving the final effect of unchanged resonant frequency, ensuring that the filtering curve of the filter remains unchanged when the ambient temperature changes.

[0108] Compared with the second example, the third example adds a second electrical isolation layer 19 and a second bias resistor layer 110 on the second electrode 13, which completely isolates the DC signal and the RF signal on both sides of the BAW resonator, so that no DC isolator is required outside the piezoelectric filter.

[0109] In some examples, an encapsulation layer 16 is further provided on a side of the second electrode 13 facing away from the base substrate 10 to isolate water vapor and oxygen to prevent device damage.

[0110] Furthermore, the material of the encapsulation layer 16 is preferably an organic compound that can isolate water vapor and oxygen, such as polyimide, epoxy resin, etc., or an inorganic material such as SiN x , Al2O3, etc. The encapsulation layer 16 can be a single layer of a single material, or a stacked configuration of multiple materials.

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

[0112] In some examples, the first bias resistor layer 17 and the second bias resistor layer 110 are both made of a conductive material with a high resistivity, preferably ITO, but may also be made of IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese copper alloy, nickel-chromium alloy, iron-chromium-aluminum alloy, or the like. The materials may be a single material or a stack of the above materials. The thickness of the first bias resistor layer 17 ranges from 1 nm to 10 μm.

[0113] In some embodiments, both the first electrical isolation layer 18 and the second electrical isolation layer 19 may be made of insulating materials, preferably Si3N4, but may also be made of SiO2, Al2O3, AlN, BN, or the like. They may be a single material or a stack of the above materials. The thickness of the electrical isolation layer ranges from 1 nm to 10 μm.

[0114] In some examples, the material of the first electrode 11 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. The material of the first electrode 11 may also be Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au, or a stack or alloy of these metals. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0115] In some examples, the material of the piezoelectric layer 12 is preferably AlN and doped AlN, such as Al (1-x) Sc x N, Al (1-x) Cr x N, Al (1-x) Y x N, Al (1-x) Ti x N, Al (1-x) Zr x N, Al (1-x) Hf x N, Al (1-x) Yb x N, Al (1-x) Ta x N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al(1-x) N, Zn 0.25 Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 N. The material of the piezoelectric layer 12 can also be selected from ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. The material of the piezoelectric layer 12 can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0116] In some examples, the material of the second electrode 13 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au may also be selected as the material of the second electrode 13. The material of the second electrode 13 may also be a stack or alloy of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0117] Next, a third example of a method for preparing a BAW resonator is described. As shown in FIG10 , the method specifically includes the following steps.

[0118] S31 , providing a base substrate 10 .

[0119] Taking the substrate 10 as an example of a single crystal silicon substrate, step S31 can specifically include: first, ultrasonically clean the single crystal silicon substrate with deionized water; then place it in a mixed solution of H2SO4:H2O=3:1, heat it to 250°C and wash it for 15 minutes; then place it in deionized water and ultrasonically clean it; then place it in a mixed solution of NH4OH:H2O=1:6, heat it to 80°C and wash it for 15 minutes; take it out and place it in deionized water for rinsing; next, place it in a mixed solution of HCl:H2O2:H2O=1:1:5, heat it to 85°C and wash it for 15 minutes, take it out and place it in dilute hydrofluoric acid of HF:H2O=1:20 and rinse it for 10 seconds to remove the surface oxide layer; finally, place it in deionized water for ultrasonic cleaning for 20 minutes, blow it dry with an air knife, and complete the entire substrate 10 cleaning process.

[0120] S32 , forming a first bias resistor layer 17 on the base substrate 10 .

[0121] Specifically, step S32 can first deposit a high-resistivity conductive material film. The deposition method is preferably radio frequency magnetron sputtering (DC magnetron sputtering is also acceptable). Alternatively, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can be selected. Alternatively, a metal foil or alloy foil can be attached. The conductive material film undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, or a dry etching process can be selected to complete the preparation of the first bias resistor layer 17.

[0122] S33 , forming a first electrical isolation layer 18 on a side of the first bias resistor layer 17 facing away from the base substrate 10 .

[0123] Specifically, step S33 may include first depositing an electrically insulating material, where the deposition method may include radio frequency controlled sputtering, pulsed laser sputtering (PLD), atomic layer deposition (ALD), or plasma chemical vapor deposition (PECVD). The electrically insulating material is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, but a dry etching process may also be selected to complete the preparation of the first electrically insulating layer 18.

[0124] S34 , forming a first electrode 11 on a side of the base substrate 10 facing away from the first electrical isolation layer 18 .

[0125] When the first electrode 11 is made of a metal material, step S34 may include depositing a first metal film on the base substrate 10. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Alternatively, a copper foil attachment method can be used. The first metal film is then subjected to a photolithography process, including glue coating (or glue spraying), pre-baking, exposure, development, and post-baking. Next, etching is performed to form a pattern including the first electrode 11. The etching process preferably adopts a wet etching process, and a dry etching process can also be selected. Finally, a de-gumming process is performed to complete the preparation of the first electrode.

[0126] S35 , forming a piezoelectric layer 12 on a side of the first electrode 11 facing away from the substrate 10 .

[0127] Taking the piezoelectric layer 12 as an example of an AlN single-layer structure, step S35 may include forming a piezoelectric material layer on the side of the first electrode 11 away from the substrate 10, and performing oriented growth of the piezoelectric material layer. The piezoelectric material layer is preferably formed by radio frequency magnetron sputtering (DC measurement and control sputtering is also acceptable). For AlN piezoelectric material, the target material is Al. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an AlN C-axis oriented piezoelectric material layer is formed, and the preferred growth orientation is (001). The deposition method of the piezoelectric material layer can also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. Next, the piezoelectric layer 12 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Etching is then performed to form a pattern including the piezoelectric layer 12. A wet etching process is preferred, but a dry etching process can also be selected. Finally, a debonding process is performed to complete the preparation of the piezoelectric layer 12 .

[0128] S36 , forming a second electrode 13 on a side of the piezoelectric layer 12 facing away from the first electrode 11 .

[0129] When the second electrode 13 is made of a metal material, step S36 may specifically include first depositing a second metal film on the side of the piezoelectric layer 12 facing away from the first electrode 11. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Next, the second metal film is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Thereafter, etching is performed to form a pattern including the second electrode 13. The etching process is preferably a wet etching process, and a dry etching process can also be selected. Finally, a de-bonding process is performed to complete the preparation of the second electrode 13.

[0130] S37 , forming a second electrical isolation layer 19 on the side of the second electrode 13 facing away from the substrate 10 .

[0131] The second electrical isolation layer 19 is formed in the same process as the first electrical isolation layer 18 , and thus will not be further described herein.

[0132] S38 , forming a second bias resistor layer 110 on the first side of the second electrical isolation layer 19 away from the base substrate 10 .

[0133] The formation process of the second bias resistor layer 110 is the same as that of the first bias resistor layer 17 , and thus will not be described again.

[0134] S39 , forming an encapsulation layer 16 on a side of the second electrode 13 facing away from the base substrate 10 .

[0135] Taking the encapsulation layer 16 as an example, the step S39 may specifically include first coating the organic material liquid, which may be done by spin coating, spraying, inkjet printing, transfer, etc., and then heating and curing to form a pattern of the encapsulation layer 16.

[0136] S310 , turning over the base substrate 10 forming the above structure, and etching to form a first cavity 101 penetrating along the thickness direction of the base substrate 10 .

[0137] In some examples, step S310 may include flipping the base substrate 10 formed with the above structure, preparing a mask pattern on the back of the base substrate 10, performing a photolithography process including resist coating (or spraying), pre-baking, exposure, development, and post-baking. HF acid wet etching is then performed to form the first cavity 101, and finally a resist stripping process is performed.

[0138] Fourth example: FIG11 is a schematic structural diagram of a bulk acoustic wave resonator of the fourth example of an embodiment of the present disclosure; as shown in FIG11 , the bulk acoustic wave resonator includes a substrate 10, and at least one layer of an acoustic reflector structure 15, a first electrode 11, a piezoelectric layer 12, and a second electrode 13 sequentially arranged on the substrate 10. The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the substrate 10 at least partially overlap. The reflector structure 15 includes a first substructure and a second substructure sequentially arranged in a direction away from the first 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 the convenience of description 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. In this case, after an RF signal enters the BAW resonator, it is converted into an acoustic wave signal through the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12. This acoustic wave then propagates longitudinally through the piezoelectric layer 12. Upon reaching the interface between the first electrode 11 and the piezoelectric layer 12, it is converted back into an RF signal through the piezoelectric effect before exiting the resonator. The first cavity 101 below the BAW resonator and the air layer above it act as acoustic reflectors, confining the acoustic signal within the resonator structure rather than dissipating it, thereby reducing losses in the BAW resonator.

[0139] When performing real-time frequency compensation, a DC bias is applied between the first electrode 11 and the second electrode 13 to generate a DC electric field in the piezoelectric layer 12. When the direction of the DC electric field is from the first electrode 11 to the second electrode 13, the electric field strength increases from 0 to +100 V / um as the DC bias increases, and the resonant frequency of the bulk acoustic wave resonator moves toward a low frequency; when the direction of the DC electric field is from the second electrode 13 to the first electrode 11, the electric field strength increases from 0 to -100 V / um as the DC bias increases, and the resonant frequency of the bulk acoustic wave resonator moves toward a high frequency. Under the action of DC electric field modulation (in order to prevent the DC signal from mixing into the RF signal and breaking down the RF circuit, a DC block needs to be added to the RF circuit outside the BAW resonator), the resonant frequency of the BAW resonator is controlled to move linearly, and the movement range is 28 to 58 ppm·f0 / (V / um). For the doped AlN piezoelectric material, the movement range is greater than that of the piezoelectric layer 12 material of the undoped AlN, where f0 is the initial resonant frequency when no DC bias is applied, and V / um is the electric field strength applied to the piezoelectric layer 12. The specific usage scenario is that when the ambient temperature changes, the resonant frequency of the BAW resonator will drift with temperature (shifting to low frequency when the temperature rises and shifting to high frequency when the temperature drops), which in turn causes the filtering curve of the filter to drift with temperature. At this time, by adjusting the DC bias applied to the piezoelectric layer 12, the resonant frequency of the BAW resonator moves in the opposite direction of the temperature drift, achieving the final effect of unchanged resonant frequency, thereby ensuring that the filtering curve of the filter remains unchanged when the ambient temperature changes.

[0140] In some examples, an encapsulation layer 16 is further provided on a side of the second electrode 13 facing away from the base substrate 10 to isolate water vapor and oxygen to prevent device damage.

[0141] Furthermore, the material of the encapsulation layer 16 is preferably an organic compound that can isolate water vapor and oxygen, such as polyimide, epoxy resin, etc., or an inorganic material such as SiN x , Al2O3, etc. The encapsulation layer 16 can be a single layer of a single material, or a stacked configuration of multiple materials.

[0142] In some examples, the material of the base substrate 10 is preferably glass, and Si, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, GaO and other materials can also be selected. The thickness of the base substrate 10 ranges from 0.1um to 10mm.

[0143] In some examples, the acoustic reflector 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 speed of sound waves propagating through it multiplied by its density. Theoretically, when the thickness of the high-acoustic impedance layer 151 is equal to one-quarter of the wavelength of sound waves at the resonant frequency of the bulk acoustic wave resonator propagating through the high-acoustic impedance layer 151, and the thickness of the low-acoustic impedance layer 152 is equal to one-quarter of the wavelength of sound waves at the resonant frequency of the bulk acoustic wave resonator propagating through the low-acoustic impedance layer 152, the alternating arrangement of high and low-acoustic impedance layers 152 (high / low / high / low, etc., or low / high / low / high, etc.) acts like an acoustic reflector, reflecting back sound signals leaking from above. The high-acoustic impedance layers 151 and the low-acoustic impedance layers 152 form a reflector structure 15. Generally, three to four groups are required to achieve a good acoustic reflection effect. Of course, the more groups, the better, but the cost will increase. There is no limit on the number of groups, and the range of reflector structures 15 can be 1 to 100 layers. There is no limit on whether it is equal to one-quarter of the wavelength, and any thickness is acceptable. The high acoustic impedance layer 151 can be made of materials such as W, Ir, Pt, Ru, Au, Mo, Ta, Ti, Cu, Ni, Zn, Al, Al2O3, and Ag. Common low acoustic impedance materials can be SiO2, Si3N4, Mg, rubber, nylon, polyimide, polyethylene, polystyrene, and Teflon. Depending on the different resonant frequencies and the different sound velocities of different materials, the thickness of a single high acoustic impedance layer 151 and a single low acoustic impedance layer 152 can range from 1 nm to 10 μm.

[0144] In some examples, the material of the first electrode 11 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. The material of the first electrode 11 may also be Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au, or a stack or alloy of these metals. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0145] In some examples, the material of the piezoelectric layer 12 is preferably AlN and doped AlN, such as Al (1-x) Sc x N, Al (1-x) Cr x N, Al (1-x) Y x N, Al (1-x) Ti x N, Al (1-x) Zr x N, Al (1-x) Hf x N, Al (1-x) Yb x N, Al (1-x) Tax N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al (1-x) N, Zn 0.25 Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 N. The material of the piezoelectric layer 12 can also be selected from ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. The material of the piezoelectric layer 12 can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0146] In some examples, the material of the second electrode 13 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au may also be selected as the material of the second electrode 13. The material of the second electrode 13 may also be a stack or alloy of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0147] Next, a fourth example of a method for preparing a BAW resonator is described. As shown in FIG12 , the method specifically includes the following steps.

[0148] S41 , providing a base substrate 10 .

[0149] Taking the base substrate 10 as an example of a single crystal silicon substrate, step S41 can specifically include: first, ultrasonically clean the single crystal silicon substrate with deionized water; then place it in a mixed solution of H2SO4:H2O=3:1, heat it to 250°C and wash it for 15 minutes; then place it in deionized water and ultrasonically clean it; then place it in a mixed solution of NH4OH:H2O=1:6, heat it to 80°C and wash it for 15 minutes; take it out and place it in deionized water for rinsing; next, place it in a mixed solution of HCl:H2O2:H2O=1:1:5, heat it to 85°C and wash it for 15 minutes, take it out and place it in dilute hydrofluoric acid of HF:H2O=1:20 and rinse it for 10 seconds to remove the surface oxide layer; finally, place it in deionized water for ultrasonic cleaning for 20 minutes, blow it dry with an air knife, and complete the entire base substrate 10 cleaning process.

[0150] S42 , forming a reflector structure 15 on the base substrate 10 .

[0151] Step S42 may specifically include: (a) first depositing the thin film material for the high acoustic impedance layer 151, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. Then, coating (or spraying) the thin film of the high acoustic impedance layer 151 with glue, pre-baking, exposure, development, post-baking, and etching to form the high acoustic impedance layer 151. The etching process preferably employs a wet etching process, or a dry etching process may also be employed. (b) then depositing the thin film material for the low acoustic impedance layer 152, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. Then, coating (or spraying) the thin film of the low acoustic impedance layer 152 with glue, pre-baking, exposure, development, post-baking, and etching to form the low acoustic impedance layer 152. The etching process is preferably a wet etching process, but a dry etching process may also be selected. Steps (a) and (b) are then repeated until an acoustic reflector structure 15 having a number of layers that meets the design requirements is obtained.

[0152] S43 , forming a first electrode 11 on the base substrate 10 .

[0153] When the first electrode 11 is made of a metal material, step S43 may include depositing a first metal film on the substrate 10. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable). Alternatively, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or copper foil attachment may be used. The first metal film is then subjected to a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Etching is then performed to form a pattern including the first electrode 11. The etching process is preferably a wet etching process, but a dry etching process may also be used. Finally, a resist stripping process is performed to complete the preparation of the first electrode.

[0154] S44 , forming a piezoelectric layer 12 on a side of the first electrode 11 facing away from the base substrate 10 .

[0155] Taking the piezoelectric layer 12 as an example of an AlN single-layer structure, step S44 may include forming a piezoelectric material layer on the side of the first electrode 11 away from the substrate 10, and performing oriented growth of the piezoelectric material layer. The piezoelectric material layer is preferably formed by radio frequency magnetron sputtering (DC measurement and control sputtering is also acceptable). For AlN piezoelectric material, the target material is Al. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an AlN C-axis oriented piezoelectric material layer is formed, and the preferred growth orientation is (001). The deposition method of the piezoelectric material layer can also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. Next, the piezoelectric layer 12 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Etching is then performed to form a pattern including the piezoelectric layer 12. A wet etching process is preferred, but a dry etching process can also be selected. Finally, a debonding process is performed to complete the preparation of the piezoelectric layer 12 .

[0156] S45 , forming a second electrode 13 on a side of the piezoelectric layer 12 facing away from the first electrode 11 .

[0157] When the second electrode 13 is made of a metal material, step S45 may specifically include first depositing a second metal film on the side of the piezoelectric layer 12 away from the first electrode 11. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Next, the second metal film is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Thereafter, etching is performed to form a pattern including the second electrode 13. The etching process is preferably a wet etching process, and a dry etching process can also be selected. Finally, a de-bonding process is performed to complete the preparation of the second electrode 13.

[0158] S46 , forming an encapsulation layer 16 on a side of the second electrode 13 facing away from the base substrate 10 .

[0159] Taking the encapsulation layer 16 as an example, the step S46 may specifically include first coating the organic material liquid, which may be done by spin coating, spraying, inkjet printing, transfer printing, etc., and then heating and curing to form a pattern of the encapsulation layer 16.

[0160] Fifth example: FIG13 is a schematic structural diagram of a bulk acoustic wave resonator of the fifth example of an embodiment of the present disclosure; as shown in FIG13 , the bulk acoustic wave resonator includes a base substrate 10, and at least one acoustic reflector structure 15, a first bias resistor layer 17, a first electrical isolation layer 18, a first electrode 11, a piezoelectric layer 12, and a second electrode 13 sequentially arranged on the base substrate 10. The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the base substrate 10 at least partially overlap. The reflector structure 15 includes a first substructure and a second substructure sequentially arranged 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 the convenience of description and understanding, the first substructure will be referred to as the high acoustic impedance layer 151 and the second substructure will be referred to as the low acoustic impedance layer 152. In this case, after an RF signal enters the BAW resonator, it is converted into an acoustic wave signal through the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12. This acoustic wave then propagates longitudinally through the piezoelectric layer 12. Upon reaching the interface between the first electrode 11 and the piezoelectric layer 12, it is converted back into an RF signal through the piezoelectric effect before exiting the resonator. The first cavity 101 below the BAW resonator and the air layer above it act as acoustic reflectors, confining the acoustic signal within the resonator structure rather than dissipating it, thereby reducing losses in the BAW resonator.

[0161] During real-time frequency compensation, a DC bias is applied between the first bias resistor layer 17 and the second electrode 13, generating a DC electric field in the piezoelectric layer 12. When the DC electric field is directed from the first bias resistor layer 17 to the second electrode 13, the electric field strength increases from 0 to +100 V / um as the DC bias increases, shifting the resonant frequency of the BAW resonator toward lower frequencies. When the DC electric field is directed from the second electrode 13 to the first bias resistor layer 17, the electric field strength increases from 0 to -100 V / um as the DC bias increases, shifting the resonant frequency of the BAW resonator toward higher frequencies. Under DC electric field modulation (to prevent DC signals from mixing into RF signals and disrupting the RF circuit, a DC block is required in the RF circuit outside the BAW resonator chip), the resonant frequency of the BAW resonator is controlled to shift linearly within a range of 28 to 58 ppm·f0 / (V / um). For doped AlN piezoelectric materials, this range is greater than for undoped AlN piezoelectric materials. Where f0 is the initial resonant frequency when no DC bias is applied, and V / um is the electric field strength applied to the piezoelectric layer 12. Specifically, when the ambient temperature changes, the resonant frequency of the BAW resonator will drift with temperature (shifting toward lower frequencies when the temperature rises and toward higher frequencies when the temperature drops), which in turn causes the filter's filtering curve to drift with temperature. At this time, by adjusting the DC bias applied to the piezoelectric layer 12, the resonant frequency of the BAW resonator shifts in the opposite direction of the temperature drift, achieving the ultimate effect of a constant resonant frequency, thus ensuring that the filter's filtering curve remains unchanged despite changes in ambient temperature.

[0162] For the fifth example, compared with the fourth example, a first bias resistor layer 17 and a first electrical isolation layer 18 are added between the first electrode 11 and the acoustic reflector structure 15 to isolate the DC signal and the RF signal in the lower half of the BAW resonator.

[0163] In some examples, an encapsulation layer 16 is further provided on a side of the second electrode 13 facing away from the base substrate 10 to isolate water vapor and oxygen to prevent device damage.

[0164] Furthermore, the material of the encapsulation layer 16 is preferably an organic compound that can isolate water vapor and oxygen, such as polyimide, epoxy resin, etc., or an inorganic material such as SiN x , Al2O3, etc. The encapsulation layer 16 can be a single layer of a single material, or a stacked configuration of multiple materials.

[0165] In some examples, the material of the base substrate 10 is preferably glass, and Si, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, GaO and other materials can also be selected. The thickness of the base substrate 10 ranges from 0.1um to 10mm.

[0166] In some examples, the acoustic reflector 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 speed of sound waves propagating through it multiplied by its density. Theoretically, when the thickness of the high-acoustic impedance layer 151 is equal to one-quarter of the wavelength of sound waves at the resonant frequency of the bulk acoustic wave resonator propagating through the high-acoustic impedance layer 151, and the thickness of the low-acoustic impedance layer 152 is equal to one-quarter of the wavelength of sound waves at the resonant frequency of the bulk acoustic wave resonator propagating through the low-acoustic impedance layer 152, the alternating arrangement of high and low-acoustic impedance layers 152 (high / low / high / low, etc., or low / high / low / high, etc.) acts like an acoustic reflector, reflecting back sound signals leaking from above. The high-acoustic impedance layers 151 and the low-acoustic impedance layers 152 form a reflector structure 15. Generally, three to four groups are required to achieve a good acoustic reflection effect. Of course, the more groups, the better, but the cost will increase. There is no limit on the number of groups, and the range of reflector structures 15 can be 1 to 100 layers. There is no limit on whether it is equal to one-quarter of the wavelength, and any thickness is acceptable. The high acoustic impedance layer 151 can be made of materials such as W, Ir, Pt, Ru, Au, Mo, Ta, Ti, Cu, Ni, Zn, Al, Al2O3, and Ag. Common low acoustic impedance materials can be SiO2, Si3N4, Mg, rubber, nylon, polyimide, polyethylene, polystyrene, and Teflon. Depending on the different resonant frequencies and the different sound velocities of different materials, the thickness of a single high acoustic impedance layer 151 and a single low acoustic impedance layer 152 can range from 1 nm to 10 μm.

[0167] In some examples, the material of the first bias resistor layer 17 is a conductive material with high resistivity, preferably ITO, but may also include IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese copper alloy, nickel-chromium alloy, iron-chromium-aluminum alloy, and the like. The material may be a single material or a stack of the above materials. The thickness of the first bias resistor layer 17 ranges from 1 nm to 10 μm.

[0168] In some embodiments, the first electrical isolation layer 18 is made of an insulating material, preferably Si3N4, but can also be made of SiO2, Al2O3, AlN, BN, etc. It can be a single material or a stack of the above materials. The thickness of the electrical isolation layer ranges from 1 nm to 10 μm.

[0169] In some examples, the material of the first electrode 11 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. The material of the first electrode 11 may also be Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au, or a stack or alloy of these metals. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0170] In some examples, the material of the piezoelectric layer 12 is preferably AlN and doped AlN, such as Al (1-x) Sc x N, Al (1-x) Cr x N, Al (1-x) Y x N, Al (1-x) Ti x N, Al (1-x) Zr x N, Al (1-x) Hf x N, Al (1-x) Yb x N, Al (1-x) Ta x N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al (1-x) N, Zn 0.25 Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 N. The material of the piezoelectric layer 12 can also be selected from ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. The material of the piezoelectric layer 12 can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0171] In some examples, the material of the second electrode 13 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au may also be selected as the material of the second electrode 13. The material of the second electrode 13 may also be a stack or alloy of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0172] Next, a fifth example of a method for preparing a BAW resonator is described. As shown in FIG14 , the method specifically includes the following steps.

[0173] S51 , providing a base substrate 10 .

[0174] Taking the base substrate 10 as an example of a single crystal silicon substrate, step S51 can specifically include: first, ultrasonically clean the single crystal silicon substrate with deionized water; then place it in a mixed solution of H2SO4:H2O=3:1, heat it to 250°C and wash it for 15 minutes; then place it in deionized water and ultrasonically clean it; then place it in a mixed solution of NH4OH:H2O=1:6, heat it to 80°C and wash it for 15 minutes; take it out and place it in deionized water for rinsing; next, place it in a mixed solution of HCl:H2O2:H2O=1:1:5, heat it to 85°C and wash it for 15 minutes, take it out and place it in dilute hydrofluoric acid of HF:H2O=1:20 and rinse it for 10 seconds to remove the surface oxide layer; finally, place it in deionized water for ultrasonic cleaning for 20 minutes, blow it dry with an air knife, and complete the entire base substrate 10 cleaning process.

[0175] S52 , forming a reflector structure 15 on the base substrate 10 .

[0176] Step S52 may specifically include: (a) first depositing the thin film material for the high acoustic impedance layer 151, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. Then, coating (or spraying) the thin film of the high acoustic impedance layer 151 with glue, pre-baking, exposure, development, post-baking, and etching to form the high acoustic impedance layer 151. The etching process preferably employs a wet etching process, or a dry etching process may also be employed. (b) then depositing the thin film material for the low acoustic impedance layer 152, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. Then, coating (or spraying) the thin film of the low acoustic impedance layer 152 with glue, pre-baking, exposure, development, post-baking, and etching to form the low acoustic impedance layer 152. The etching process is preferably a wet etching process, but a dry etching process may also be selected. Steps (a) and (b) are then repeated until an acoustic reflector structure 15 having a number of layers that meets the design requirements is obtained.

[0177] S53 , forming a first bias resistor layer 17 on a side of the reflector structure 15 facing away from the substrate 10 .

[0178] Specifically, step S53 can first deposit a high-resistivity conductive material film. The deposition method is preferably radio frequency magnetron sputtering (DC magnetron sputtering is also acceptable). Alternatively, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can be selected. Alternatively, a metal foil or alloy foil can be attached. The conductive material film undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, and a dry etching process can also be selected to complete the preparation of the first bias resistor layer 17.

[0179] S54 , forming a first electrical isolation layer 18 on a side of the first bias resistor layer 17 facing away from the base substrate 10 .

[0180] Specifically, step S54 may include first depositing an electrically insulating material. The deposition method may include radio frequency controlled sputtering, pulsed laser sputtering (PLD), atomic layer deposition (ALD), or plasma chemical vapor deposition (PECVD). The electrically insulating material undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably using a wet etching process, but a dry etching process may also be selected, to complete the preparation of the first electrically insulating layer 18.

[0181] S55 , forming a first electrode 11 on the first electrical isolation layer 18 facing away from the base substrate 10 .

[0182] When the first electrode 11 is made of a metal material, step S55 may include depositing a first metal film on the base substrate 10. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Alternatively, a copper foil attachment method can be used. The first metal film is then subjected to a photolithography process, including glue coating (or glue spraying), pre-baking, exposure, development, and post-baking. Next, etching is performed to form a pattern including the first electrode 11. The etching process preferably adopts a wet etching process, and a dry etching process can also be selected. Finally, a de-bonding process is performed to complete the preparation of the first electrode.

[0183] S56 , forming a piezoelectric layer 12 on a side of the first electrode 11 facing away from the base substrate 10 .

[0184] Taking the piezoelectric layer 12 as an example of an AlN single-layer structure, step S56 may include forming a piezoelectric material layer on the side of the first electrode 11 away from the substrate 10, and performing oriented growth of the piezoelectric material layer. The piezoelectric material layer is preferably formed by radio frequency magnetron sputtering (DC measurement and control sputtering is also acceptable). For AlN piezoelectric material, the target material is Al. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an AlN C-axis oriented piezoelectric material layer is formed, and the preferred growth orientation is (001). The deposition method of the piezoelectric material layer can also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. Next, the piezoelectric layer 12 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Etching is then performed to form a pattern including the piezoelectric layer 12. A wet etching process is preferred, but a dry etching process can also be selected. Finally, a debonding process is performed to complete the preparation of the piezoelectric layer 12 .

[0185] S57 . Form a second electrode 13 on a side of the piezoelectric layer 12 facing away from the first electrode 11 .

[0186] When the second electrode 13 is made of a metal material, step S57 may specifically include first depositing a second metal film on the side of the piezoelectric layer 12 facing away from the first electrode 11. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Next, the second metal film is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Thereafter, etching is performed to form a pattern including the second electrode 13. The etching process is preferably a wet etching process, and a dry etching process can also be selected. Finally, a de-bonding process is performed to complete the preparation of the second electrode 13.

[0187] S58 , forming an encapsulation layer 16 on a side of the second electrode 13 facing away from the base substrate 10 .

[0188] Taking the encapsulation layer 16 as an example, the step S58 may specifically include first coating the organic material liquid, which may be done by spin coating, spraying, inkjet printing, transfer printing, etc., and then heating and curing to form a pattern of the encapsulation layer 16.

[0189] Sixth example: Figure 15 is a schematic structural diagram of a bulk acoustic wave resonator of the sixth example of an embodiment of the present disclosure; as shown in Figure 15, the bulk acoustic wave resonator includes a base substrate 10, and at least one layer of an acoustic reflector structure 15, a first bias resistor layer 17, a first electrical isolation layer 18, a first electrode 11, a piezoelectric layer 12, a second electrode 13, a second electrical isolation layer 19, and a second bias resistor layer 110, which are sequentially arranged on the base substrate 10. The orthographic projections of any two of the first electrode 11, the piezoelectric layer 12, and the second electrode 13 on the base substrate 10 at least partially overlap. Among them, the reflector structure 15 includes a first substructure and a second substructure sequentially arranged 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 the convenience of description and understanding, the first substructure is referred to as the high acoustic impedance layer 151 and the second substructure is referred to as the low acoustic impedance layer 152. In this case, after an RF signal enters the BAW resonator, it is converted into an acoustic wave signal through the inverse piezoelectric effect at the interface between the second electrode 13 and the piezoelectric layer 12. This acoustic wave then propagates longitudinally through the piezoelectric layer 12. Upon reaching the interface between the first electrode 11 and the piezoelectric layer 12, it is converted back into an RF signal through the piezoelectric effect before exiting the resonator. The first cavity 101 below the BAW resonator and the air layer above it act as acoustic reflectors, confining the acoustic signal within the resonator structure rather than dissipating it, thereby reducing losses in the BAW resonator.

[0190] During real-time frequency compensation, a DC bias is applied between the first bias resistor layer 17 and the second bias resistor layer 110, generating a DC electric field in the piezoelectric layer 12. When the DC electric field is directed from the first bias resistor layer 17 to the second bias resistor layer 110, the electric field strength increases from 0 to +100 V / um as the DC bias increases, shifting the resonant frequency of the BAW resonator toward lower frequencies. When the DC electric field is directed from the second bias resistor layer 110 to the first bias resistor layer 17, the electric field strength increases from 0 to -100 V / um as the DC bias increases, shifting the resonant frequency of the BAW resonator toward higher frequencies. Under DC field modulation, the resonant frequency of the BAW resonator is controlled to shift linearly within a range of 28 to 58 ppm·f0 / (V / um). For doped AlN piezoelectric materials, the shift range is greater than for undoped AlN piezoelectric materials. f0 is the initial resonant frequency without a DC bias, and V / um is the electric field strength applied to the piezoelectric layer 12. The specific usage scenario is that when the ambient temperature changes, the resonant frequency of the bulk acoustic wave resonator will drift with temperature (shift to low frequency when the temperature rises, and shift to high frequency when the temperature drops), which in turn causes the filtering curve of the filter to drift with temperature. At this time, by adjusting the DC bias applied to the piezoelectric layer 12, the resonant frequency of the bulk acoustic wave resonator moves in the opposite direction of the temperature drift, achieving the final effect of unchanged resonant frequency, ensuring that the filtering curve of the filter remains unchanged when the ambient temperature changes.

[0191] Compared with the fifth example, the sixth example adds a second electrical isolation layer 19 and a second bias resistor layer 110 on the second electrode 13, which completely isolates the DC signal and the RF signal on both sides of the BAW resonator, so that no DC isolator is required outside the piezoelectric filter.

[0192] In some examples, an encapsulation layer 16 is further provided on a side of the second electrode 13 facing away from the base substrate 10 to isolate water vapor and oxygen to prevent device damage.

[0193] Furthermore, the material of the encapsulation layer 16 is preferably an organic compound that can isolate water vapor and oxygen, such as polyimide, epoxy resin, etc., or an inorganic material such as SiN x , Al2O3, etc. The encapsulation layer 16 can be a single layer of a single material, or a stacked configuration of multiple materials.

[0194] In some examples, the material of the base substrate 10 is preferably glass, and Si, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, GaO and other materials can also be selected. The thickness of the base substrate 10 ranges from 0.1um to 10mm.

[0195] In some examples, the acoustic reflector 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 speed of sound waves propagating through it multiplied by its density. Theoretically, when the thickness of the high-acoustic impedance layer 151 is equal to one-quarter of the wavelength of sound waves at the resonant frequency of the bulk acoustic wave resonator propagating through the high-acoustic impedance layer 151, and the thickness of the low-acoustic impedance layer 152 is equal to one-quarter of the wavelength of sound waves at the resonant frequency of the bulk acoustic wave resonator propagating through the low-acoustic impedance layer 152, the alternating arrangement of high and low-acoustic impedance layers 152 (high / low / high / low, etc., or low / high / low / high, etc.) acts like an acoustic reflector, reflecting back sound signals leaking from above. The high-acoustic impedance layers 151 and the low-acoustic impedance layers 152 form a reflector structure 15. Generally, three to four groups are required to achieve a good acoustic reflection effect. Of course, the more groups, the better, but the cost will increase. There is no limit on the number of groups, and the range of reflector structures 15 can be 1 to 100 layers. There is no limit on whether it is equal to one-quarter of the wavelength, and any thickness is acceptable. The high acoustic impedance layer 151 can be made of materials such as W, Ir, Pt, Ru, Au, Mo, Ta, Ti, Cu, Ni, Zn, Al, Al2O3, and Ag. Common low acoustic impedance materials can be SiO2, Si3N4, Mg, rubber, nylon, polyimide, polyethylene, polystyrene, and Teflon. Depending on the different resonant frequencies and the different sound velocities of different materials, the thickness of a single high acoustic impedance layer 151 and a single low acoustic impedance layer 152 can range from 1 nm to 10 μm.

[0196] In some examples, the first bias resistor layer 17 and the second bias resistor layer 110 can both be made of a conductive material with a high resistivity, preferably ITO, but can also be made of IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese copper alloy, nickel-chromium alloy, iron-chromium-aluminum alloy, or the like. The materials can be a single material or a stack of the above materials. The thickness of the first bias resistor layer 17 ranges from 1 nm to 10 μm.

[0197] In some embodiments, the materials of the first electrical isolation layer 18 and the second electrical isolation layer 19 can be insulating materials, preferably Si3N4, but can also be SiO2, Al2O3, AlN, BN, etc., and can be a single material or a stack of the above materials. The thickness of the electrical isolation layer ranges from 1 nm to 10 μm.

[0198] In some examples, the material of the first electrode 11 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. The material of the first electrode 11 may also be Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au, or a stack or alloy of these metals. The thickness of the first electrode 11 ranges from 1 nm to 10 μm.

[0199] In some examples, the material of the piezoelectric layer 12 is preferably AlN and doped AlN, such as Al (1-x) Sc x N, Al (1-x) Cr x N, Al (1-x) Y x N, Al (1-x) Ti x N, Al (1-x) Zr x N, Al (1-x) Hf x N, Al (1-x) Yb x N, Al (1-x) Ta x N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al (1-x) N, Zn 0.25 Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 N. The material of the piezoelectric layer 12 can also be selected from ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14, BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF, etc. The material of the piezoelectric layer 12 can be a single piezoelectric material or a stack of the above piezoelectric materials. The thickness of the piezoelectric layer 12 ranges from 10nm to 100um.

[0200] In some examples, the material of the second electrode 13 is preferably metallic molybdenum, as its lattice size closely matches the lattice structure and size of AlN and doped AlN, the materials of the piezoelectric layer 12. Al, Cu, Co, Ag, Ti, Pt, Ru, W, or Au may also be selected as the material of the second electrode 13. The material of the second electrode 13 may also be a stack or alloy of the above metals. The thickness of the second electrode 13 ranges from 1 nm to 10 μm.

[0201] Next, a sixth example of a method for preparing a BAW resonator is described. As shown in FIG16 , the method specifically includes the following steps.

[0202] S61 , providing a base substrate 10 .

[0203] Taking the base substrate 10 as an example, step S61 can specifically include: first, ultrasonically clean the single crystal silicon substrate with deionized water; then place it in a mixed solution of H2SO4:H2O=3:1, heat it to 250°C and wash it for 15 minutes; then place it in deionized water and ultrasonically clean it; then place it in a mixed solution of NH4OH:H2O=1:6, heat it to 80°C and wash it for 15 minutes; take it out and place it in deionized water for rinsing; next, place it in a mixed solution of HCl:H2O2:H2O=1:1:5, heat it to 85°C and wash it for 15 minutes, take it out and place it in dilute hydrofluoric acid of HF:H2O=1:20 and rinse it for 10 seconds to remove the surface oxide layer; finally, place it in deionized water for ultrasonic cleaning for 20 minutes, blow it dry with an air knife, and complete the entire base substrate 10 cleaning process.

[0204] S62 , forming a reflector structure 15 on the base substrate 10 .

[0205] Step S62 may specifically include: (a) first depositing the thin film material for the high acoustic impedance layer 151, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or the like. Then, coating (or spraying) the thin film of the high acoustic impedance layer 151 with glue, pre-baking, exposure, development, post-baking, and etching to form the high acoustic impedance layer 151. The etching process is preferably a wet etching process, or a dry etching process may also be used. (b) then depositing the thin film material for the low acoustic impedance layer 152, preferably by DC magnetron sputtering (RF magnetron sputtering is also acceptable), or alternatively by pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, or the like. Then, coating (or spraying) the thin film of the low acoustic impedance layer 152 with glue, pre-baking, exposure, development, post-baking, and etching to form the low acoustic impedance layer 152. The etching process is preferably a wet etching process, but a dry etching process may also be selected. Steps (a) and (b) are then repeated until an acoustic reflector structure 15 having a number of layers that meets the design requirements is obtained.

[0206] S63 , forming a first bias resistor layer 17 on a side of the reflector structure 15 facing away from the substrate 10 .

[0207] Specifically, step S63 can first deposit a high-resistivity conductive material film. The deposition method is preferably radio frequency magnetron sputtering (DC magnetron sputtering is also acceptable). Alternatively, pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can be selected. Alternatively, a metal foil or alloy foil can be attached. The conductive material film undergoes a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably a wet etching process, and a dry etching process can also be selected to complete the preparation of the first bias resistor layer 17.

[0208] S64 , forming a first electrical isolation layer 18 on a side of the first bias resistor layer 17 facing away from the base substrate 10 .

[0209] Specifically, step S64 may include first depositing an electrically insulating material. The deposition method may include radio frequency controlled sputtering, pulsed laser sputtering (PLD), atomic layer deposition (ALD), or plasma chemical vapor deposition (PECVD). The electrically insulating material undergoes a photolithography process, including resist coating (or spraying), pre-baking, exposure, development, and post-baking. Finally, etching is performed, preferably using a wet etching process, but a dry etching process may also be selected, to complete the preparation of the first electrically insulating layer 18.

[0210] S65 , forming a first electrode 11 on the first electrical isolation layer 18 facing away from the base substrate 10 .

[0211] When the first electrode 11 is made of a metal material, step S65 may include depositing a first metal film on the base substrate 10. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Alternatively, a copper foil attachment method can be used. The first metal film is then subjected to a photolithography process, including glue coating (or glue spraying), pre-baking, exposure, development, and post-baking. Next, etching is performed to form a pattern including the first electrode 11. The etching process preferably adopts a wet etching process, and a dry etching process can also be selected. Finally, a de-gumming process is performed to complete the preparation of the first electrode.

[0212] S66 , forming a piezoelectric layer 12 on a side of the first electrode 11 facing away from the base substrate 10 .

[0213] Taking the piezoelectric layer 12 as an example of an AlN single-layer structure, step S56 may include forming a piezoelectric material layer on the side of the first electrode 11 away from the substrate 10, and performing oriented growth of the piezoelectric material layer. The piezoelectric material layer is preferably formed by radio frequency magnetron sputtering (DC measurement and control sputtering is also acceptable). For AlN piezoelectric material, the target material is Al. By controlling the Ar and N2 gas pressures and temperatures during the deposition process and the post-annealing time and temperature, an AlN C-axis oriented piezoelectric material layer is formed, and the preferred growth orientation is (001). The deposition method of the piezoelectric material layer can also be selected from pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), metal organic chemical vapor deposition (MOCVD), plasma enhanced chemical vapor deposition (PECVD), etc. Next, the piezoelectric layer 12 is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Etching is then performed to form a pattern including the piezoelectric layer 12. A wet etching process is preferred, but a dry etching process can also be selected. Finally, a debonding process is performed to complete the preparation of the piezoelectric layer 12 .

[0214] S67 . Form a second electrode 13 on a side of the piezoelectric layer 12 facing away from the first electrode 11 .

[0215] When the second electrode 13 is made of a metal material, step S67 may specifically include first depositing a second metal film on the side of the piezoelectric layer 12 facing away from the first electrode 11. The deposition method is preferably DC magnetron sputtering (RF magnetron sputtering is also acceptable), and pulsed laser sputtering (PLD), molecular beam epitaxy (MBE), thermal evaporation, electron beam evaporation, etc. can also be selected. Next, the second metal film is subjected to a photolithography process, including coating (or spraying), pre-baking, exposure, development, and post-baking. Thereafter, etching is performed to form a pattern including the second electrode 13. The etching process is preferably a wet etching process, and a dry etching process can also be selected. Finally, a de-bonding process is performed to complete the preparation of the second electrode 13.

[0216] S68 , forming a second electrical isolation layer 19 on the side of the second electrode 13 facing away from the substrate 10 .

[0217] The second electrical isolation layer 19 is formed in the same process as the first electrical isolation layer 18 , and thus will not be further described herein.

[0218] S69 , forming a second bias resistor layer 110 on the first side of the second electrical isolation layer 19 away from the base substrate 10 .

[0219] The formation process of the second bias resistor layer 110 is the same as that of the first bias resistor layer 17 , and thus will not be described again.

[0220] S610 , forming an encapsulation layer 16 on a side of the second electrode 13 facing away from the base substrate 10 .

[0221] Taking the encapsulation layer 16 as an example, the step S610 may specifically include first coating the organic material liquid, which may be done by spin coating, spraying, inkjet printing, transfer printing, etc., and then heating and curing to form a pattern of the encapsulation layer 16.

[0222] It should be noted that, in the above-mentioned example of the bulk acoustic wave resonator, only the first electrical isolation layer 18 and the first bias resistor layer 17 are formed on the side of the first electrode 11 close to the substrate 10, and the first electrical isolation layer 18 and the first bias resistor layer 17 are formed on the side of the first electrode 11 close to the substrate 10, and the second electrical isolation layer 19 and the second bias resistor layer 110 are formed on the side of the second electrode 13 away from the substrate 10. It should be understood that it is also feasible to form the second electrical isolation layer 19 and the second bias resistor layer 110 only on the side of the second electrode 13 away from the substrate 10.

[0223] An embodiment of the present disclosure further provides an electronic device, which may include any of the above-mentioned bulk acoustic wave resonators.

[0224] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A bulk acoustic wave resonator, comprising: A substrate, a first electrode, a piezoelectric layer, and a second electrode; The first electrode is arranged on the substrate, the second electrode is arranged on a side of the first electrode away from the substrate, the piezoelectric layer is arranged between the first electrode and the second electrode, and the orthographic projections of any two of the first electrode, the piezoelectric layer and the second electrode on the substrate at least partially overlap; wherein the bulk acoustic wave filter further includes: A first bias resistor layer is arranged on the side of the first electrode close to the substrate, and a first electrical isolation layer is arranged between the first bias resistor layer and the first electrode; the material of the first bias resistor layer is a high resistivity material; and / or, A second bias resistor layer is arranged on the side of the second electrode away from the substrate, and a second electrical isolation layer is arranged between the second bias resistor layer and the second electrode; the material of the second bias resistor layer is a high resistivity material.

2. The BAW resonator according to claim 1, wherein: The base substrate has a first cavity penetrating along a thickness direction thereof.

3. The BAW resonator according to claim 1, wherein: It also includes at least one layer of reflector structure arranged on a side of the substrate close to the first electrode; when the substrate is provided with the first bias resistor layer, the reflector structure is arranged on a side of the first bias resistor layer close to the substrate; The reflector structure comprises a first substructure layer and a second substructure layer which are sequentially arranged in a direction away from the substrate, and the acoustic impedance of the material of the first substructure layer is greater than the acoustic impedance of the material of the second substructure layer.

4. The BAW resonator according to claim 1, wherein: When the BAW resonator includes the first bias resistor layer, the material of the first bias resistor layer includes a single-layer structure of any one of ITO, IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese-copper alloy, nickel-chromium alloy, and iron-chromium-aluminum alloy, or a stacked-layer structure of multiple materials.

5. The BAW resonator according to claim 1, wherein: When the BAW resonator includes the second bias resistor layer, the second bias resistor layer includes a single-layer structure of any one of ITO, IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese-copper alloy, nickel-chromium alloy, and iron-chromium-aluminum alloy, or a stacked-layer structure of multiple materials.

6. The BAW resonator according to claim 1, wherein: When the BAW resonator includes the first electrical isolation layer, the material of the first electrical isolation layer includes a single-layer structure of any one material among Si3N4, SiO2, Al2O3, AlN, and BN, or a stacked-layer structure of multiple materials.

7. The BAW resonator according to claim 1, wherein: When the BAW resonator includes the second electrical isolation layer, the material of the second electrical isolation layer includes a single-layer structure of any one material among Si3N4, SiO2, Al2O3, AlN, and BN, or a stacked-layer structure of multiple materials.

8. The BAW resonator according to claim 1, wherein: The substrate includes any one of glass, Si, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, and GaO.

9. The BAW resonator according to claim 1, wherein: The piezoelectric material includes AlN, doped AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF; wherein the doped AlN includes Al (1-x) Sc x N、Al (1-x) Cr x N、Al (1-x) Y x N、Al (1-x) Ti x N、Al (1-x) Zr x N、Al (1-x) Hf x N、Al (1-x) Yb x N、Al (1-x) Ta x N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al (1-x) N, Zn 0.25 Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 Any one of N.

10. The BAW resonator according to claim 1, wherein: The first electrode and the second electrode both include any one of Mo, Al, Cu, Co, Ag, Ti, Pt, Ru, W, and Au.

11. A method for preparing a bulk acoustic wave resonator, comprising: The step of sequentially forming a first electrode, a piezoelectric layer and a second electrode on a first base substrate, wherein the orthographic projections of any two of the first electrode, the piezoelectric layer and the second electrode on the first base substrate at least partially overlap; wherein The preparation method further includes: forming a first A bias resistor layer, and a first electrical isolation layer is formed between the first bias resistor layer and the first electrode; the material of the first bias resistor layer is a high resistivity material; and / or, A second bias resistor layer is formed on the side of the second electrode away from the base substrate, and a second electrical isolation layer is formed between the second bias resistor layer and the second electrode; the material of the second bias resistor layer is a high resistivity material.

12. The method for preparing a bulk acoustic wave resonator according to claim 11, wherein: Also includes: The base substrate is processed to form a first cavity penetrating along a thickness direction of the base substrate.

13. The method for preparing a bulk acoustic wave resonator according to claim 11, wherein: At least one layer of reflector structure is formed on a side of the base substrate close to the first electrode; when the first bias resistor layer is formed on the base substrate, the reflector structure is formed on a side of the first bias resistor layer close to the base substrate; Forming the reflector structure includes sequentially forming a first substructure layer and a second substructure layer in a direction away from the substrate, and the acoustic impedance of the material of the first substructure layer is greater than the acoustic impedance of the material of the second substructure layer.

14. The method for preparing a bulk acoustic wave resonator according to claim 11, wherein: When the BAW resonator includes the first bias resistor layer, the material of the first bias resistor layer includes a single-layer structure of any one of ITO, IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese-copper alloy, nickel-chromium alloy, and iron-chromium-aluminum alloy, or a stacked-layer structure of multiple materials.

15. The method for preparing a bulk acoustic wave resonator according to claim 11, wherein: When the BAW resonator includes the second bias resistor layer, the second bias resistor layer includes a single-layer structure of any one material of ITO, IZO, ZnO, IGO, IGZO, W, Mn, Cr, Ti, Ni, constantan alloy, manganese-copper alloy, nickel-chromium alloy, and iron-chromium-aluminum alloy, or a stacked-layer structure of multiple materials.

16. The method for preparing a bulk acoustic wave resonator according to claim 11, wherein: When the BAW resonator includes the first electrical isolation layer, the material of the first electrical isolation layer includes a single-layer structure of any one of Si3N4, SiO2, Al2O3, AlN, and BN, or a stacked-layer structure of multiple materials.

17. The method for preparing a bulk acoustic wave resonator according to claim 11, wherein: When the BAW resonator includes the second electrical isolation layer, the material of the second electrical isolation layer includes a single-layer structure of any one material among Si3N4, SiO2, Al2O3, AlN, and BN, or a stacked-layer structure of multiple materials.

18. The method for preparing a bulk acoustic wave resonator according to claim 11, wherein: The substrate includes any one of glass, Si, sapphire, SiC, GaAs, GaN, InP, BN, ZnO, and GaO.

19. The method for preparing a bulk acoustic wave resonator according to claim 11, wherein: The piezoelectric material includes AlN, doped AlN, ZnO, PZT, GaN, InN, CdS, CdSe, ZnS, CdTe, ZnTe, GaAs, GaSb, InAs, InSb, GaSe, GaP, AlP, quartz crystal, LiTaO3, LiNbO3, La3Ga5SiO 14 , BaTiO3, PbNb2O6, PBLN, LiGaO3, LiGeO3, TiGeO3, PbTiO3, PbZrO3, PVDF; wherein the doped AlN includes Al (1-x) Sc x N、Al (1-x) Cr x N、Al (1-x) Y x N、Al (1-x) Ti x N、Al (1-x) Zr x N、Al (1-x) Hf x N、Al (1-x) Yb x N、Al (1-x) Ta x N, Mg 0.5x Nb 0.5x Al (1-x) N, Mg 0.5x Ti 0.5x Al (1-x) N, Mg 0.5x Zr 0.5x Al (1-x) N, Mg 0.5x Hf 0.5x Al (1-x) N, Mg 0.5x Si 0.5x Al (1-x) N, Zn 0.25 Ti 0.25 Al 0.5 N, Zn 0.25 Zr 0.25 Al 0.5 N, Zn 0.25 Hf 0.25 Al 0.5 Any one of N.

20. The method for preparing a bulk acoustic wave resonator according to claim 11, wherein: The first electrode and the second electrode both include any one of Mo, Al, Cu, Co, Ag, Ti, Pt, Ru, W, and Au.

21. An electronic device comprising the BAW resonator according to any one of claims 1 to 10.

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