A method for forming a bulk acoustic wave resonance device

Abstract

A method for forming a bulk acoustic wave resonator device, comprising: forming a first layer, including: providing a first substrate; forming a piezoelectric layer, located on the first substrate; forming a first electrode layer, located on the piezoelectric layer; forming a cavity pretreatment layer, located on the piezoelectric layer, for forming a cavity, the cavity pretreatment layer at least covering the first end of the first electrode layer, wherein the first side of the first layer corresponds to the first substrate side, and the second side of the first layer corresponds to the cavity pretreatment layer side (S201); forming a second layer, including: providing a second substrate (S203); connecting the first layer and the second layer, wherein the second layer is located on the second side (S205); removing the first substrate, the first side corresponding to the piezoelectric layer side (S207); forming a second electrode layer, located on the first side, contacting the piezoelectric layer (S209); and removing the second layer (S213). In this way, the piezoelectric layer does not include crystals with obvious steering, thereby helping to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device. In addition, removing the second substrate can eliminate the electrical loss caused by it.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a method for forming a bulk acoustic wave resonance device. Background Art

[0002] The RF (Radio Frequency, RF) front-end chips of wireless communication equipment include power amplifiers, antenna switches, RF filters, duplexers, multiplexers and low noise amplifiers, etc. Among them, RF filters include surface acoustic wave (Surface Acoustic Wave, SAW) filters, bulk acoustic wave (Bulk Acoustic Wave, BAW) filters, micro-electro-mechanical system (Micro-Electro-Mechanical System, MEMS) filters, integrated passive devices (Integrated Passive Devices, IPD), etc. The quality factor value (Q value) of SAW resonators and BAW resonators is relatively high. The low insertion loss and high out-of-band suppression RF filters made of SAW resonators and BAW resonators, namely SAW filters and BAW filters, are the mainstream RF filters currently used in wireless communication equipment such as mobile phones and base stations. Among them, the Q value is the quality factor value of the resonator, which is defined as the center frequency divided by the 3dB bandwidth of the resonator. The operating frequency of SAW filters is generally 0.4GHz to 2.7GHz, and the operating frequency of BAW filters is generally 0.7GHz to 7GHz.

[0003] Compared with SAW resonators, BAW resonators have better performance, but due to the complex process steps, the manufacturing cost of BAW resonators is higher than that of SAW resonators. However, as wireless communication technology gradually evolves, more and more frequency bands are used. At the same time, with the application of frequency band superposition technologies such as carrier aggregation, the mutual interference between wireless frequency bands has become more and more serious. High-performance BAW technology can solve the problem of mutual interference between frequency bands. With the advent of the 5G era, wireless mobile networks have introduced higher communication frequency bands. Currently, only BAW technology can solve the filtering problem of high-frequency bands.

[0004] Figure 1aA BAW filter circuit is shown, including a ladder circuit composed of multiple BAW resonators, wherein f1, f2, f3, and f4 represent four different frequencies, respectively. In each BAW resonator, the metal electrodes on both sides of the piezoelectric layer of the resonator generate alternating positive and negative voltages, and the piezoelectric layer generates sound waves through the alternating positive and negative voltages. The sound waves in the resonator propagate in a direction perpendicular to the piezoelectric layer. In order to form resonance, the sound wave needs to be totally reflected at the upper surface of the upper metal electrode and the lower surface of the lower metal electrode to form a standing sound wave. The condition for the reflection of the sound wave is that the acoustic impedance of the contact area with the upper surface of the upper metal electrode and the lower surface of the lower metal electrode is significantly different from the acoustic impedance of the metal electrode.

[0005] Film Bulk Acoustic Wave Resonator (FBAR) is a BAW resonator that can confine the energy of acoustic waves within the device. The resonator has air above the resonance area and a cavity below. The acoustic impedance of air is quite different from that of metal electrodes, so the acoustic waves can be fully reflected on the upper surface of the upper metal electrode and the lower surface of the lower metal electrode, forming standing waves.

[0006] Figure 1b A schematic cross-sectional structure diagram of an FBAR 100 is shown. The FBAR 100 includes: a substrate 101, the substrate 101 includes a cavity 101a; and an active layer 103, located on the substrate 101. The active layer 103 includes a piezoelectric layer 105 and electrode layers 107 (i.e., a lower electrode layer) and 109 (i.e., an upper electrode layer) located on both sides of the piezoelectric layer 105, respectively, wherein the electrode layer 107 contacts the substrate 101. The FBAR 100 is formed by stacking layer by layer, that is, the electrode layer 107 is formed on the substrate 101, the piezoelectric layer 105 is formed on the electrode layer 107, and then the electrode layer 109 is formed on the piezoelectric layer 105. Since the electrode layer 107 is raised, forming the piezoelectric layer 105 directly on the electrode layer 107 will cause some crystals in the piezoelectric layer 105 (for example, crystals at both side edges of the piezoelectric layer 105 in the horizontal direction) to turn significantly and become non-parallel to other crystals, thereby reducing the electromechanical coupling coefficient and Q value of the FBAR. In addition, the substrate 101 will cause electrical loss. Summary of the invention

[0007] The problem solved by the present invention is to provide a method for forming a bulk acoustic wave resonator, which can make the piezoelectric layer not include crystals with obvious turning, thereby helping to improve the electromechanical coupling coefficient of the resonator and the Q value of the resonator. In addition, the method for forming the resonator can eliminate the electrical loss caused by the substrate.

[0008] To solve the above problems, an embodiment of the present invention provides a method for forming a bulk acoustic wave resonance device, comprising: forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers the first end of the first electrode layer, and the cavity pretreatment layer contacts the piezoelectric layer, wherein the first side of the first layer corresponds to the first substrate side, and the second side of the first layer corresponds to the cavity pretreatment layer side; forming a second layer, wherein the forming of the second layer comprises: providing a second substrate; bonding the first layer and the second layer, wherein the second layer is located on the second side; removing the first substrate, wherein the first side corresponds to the piezoelectric layer side; forming a second electrode layer, which is located on the first side and contacts the piezoelectric layer; and removing the second layer.

[0009] It should be noted that the piezoelectric layer is formed on the first substrate, and the surface of the first substrate is flat, so the piezoelectric layer does not include crystals with obvious turning, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device. In addition, removing the second substrate can eliminate the electrical loss caused by the second substrate.

[0010] In some embodiments, the forming of the cavity pretreatment layer includes: forming a sacrificial layer, which is located on the piezoelectric layer, and the sacrificial layer covers the first end. In some embodiments, the material of the sacrificial layer includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, polysilicon. In some embodiments, the polymer includes but is not limited to at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0011] In some embodiments, the forming of the cavity pretreatment layer further includes: forming a first intermediate layer, located above the piezoelectric layer, the first intermediate layer at least covering the sacrificial layer, and the second side corresponds to the first intermediate layer side. In some embodiments, the material of the first intermediate layer includes but is not limited to at least one of the following: polymer, insulating dielectric. In some embodiments, the polymer includes but is not limited to at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), polyimide. In some embodiments, the insulating dielectric includes but is not limited to at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide. In some embodiments, the thickness of the first intermediate layer includes but is not limited to: 20 microns to 100 microns. In some embodiments, the first intermediate layer also covers the second end of the first electrode layer. It should be noted that the acoustic impedance of the first intermediate layer may be small.

[0012] In some embodiments, the piezoelectric layer includes a plurality of crystals, and the plurality of crystals include a first crystal and a second crystal, wherein the first crystal and the second crystal are any two crystals of the plurality of crystals; a first coordinate axis along a first direction corresponds to a height of the first crystal, and a second coordinate axis along a second direction corresponds to a height of the second crystal, wherein the first direction and the second direction are the same or opposite. It should be noted that the first direction and the second direction are the same means that the angle between the vector along the first direction and the vector along the second direction ranges from 0 degrees to 5 degrees; the first direction and the second direction are opposite means that the angle between the vector along the first direction and the vector along the second direction ranges from 175 degrees to 180 degrees.

[0013] In some embodiments, the first crystal corresponds to a first coordinate system, which includes the first coordinate axis and a third coordinate axis along a third direction; the second crystal corresponds to a second coordinate system, which includes the second coordinate axis and a fourth coordinate axis along a fourth direction.

[0014] In some embodiments, the first coordinate system further includes a fifth coordinate axis along a fifth direction, and the second coordinate system further includes a sixth coordinate axis along a sixth direction. In some embodiments, the first direction is the same as or opposite to the second direction, and the third direction is the same as or opposite to the fourth direction. It should be noted that the third direction is the same as the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 0 degrees to 5 degrees; the third direction is opposite to the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 175 degrees to 180 degrees.

[0015] In some embodiments, the material of the piezoelectric layer includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

[0016] In some embodiments, the piezoelectric layer includes a plurality of crystals, and the half-peak width of the rocking curve of the plurality of crystals is less than 2.5 degrees. It should be noted that the rocking curve describes the angular divergence of a particular crystal plane (the crystal plane determined by the diffraction angle) in the sample, and is represented by a plane coordinate system, wherein the horizontal axis is the angle between the crystal plane and the sample plane, and the vertical axis represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the lattice quality, and the smaller the half-peak width angle, the better the lattice quality. In addition, the full width at half maximum (FWHM) refers to the distance between the two points where the function value is equal to half of the peak value in a peak of the function.

[0017] In some embodiments, joining the first layer and the second layer comprises: bonding the first intermediate layer and the second substrate. In some embodiments, bonding the first intermediate layer and the second substrate comprises: applying pressure to the first intermediate layer and the second substrate to bond the first intermediate layer and the second substrate.

[0018] In some embodiments, removing the second layer includes: removing the second substrate by grinding.

[0019] In some embodiments, the method for forming the resonant device further includes: removing the sacrificial layer to form the cavity, wherein the first end is located in the cavity.

[0020] In some embodiments, the forming of the second layer further comprises: forming a second intermediate layer, which is located on the second substrate. In some embodiments, the material of the second intermediate layer includes, but is not limited to, a chemical with low surface energy. In some embodiments, the chemical with low surface energy includes, but is not limited to, at least one of the following: 1H, 1H, 2H, 2H-perfluoroheptadecanetrimethyloxysilane, polydimethylsiloxane, hydrocarbons, fluorocarbons, polyethylene, polypropylene, polytetrafluoroethylene. In some embodiments, joining the first layer and the second layer comprises: bonding the cavity pretreatment layer and the second intermediate layer. In some embodiments, bonding the cavity pretreatment layer and the second intermediate layer comprises: applying pressure to the cavity pretreatment layer and the second intermediate layer so that the cavity pretreatment layer and the second intermediate layer are bonded. In some embodiments, removing the second layer comprises: separating the cavity pretreatment layer and the second intermediate layer, and removing the second intermediate layer and the second substrate. In some embodiments, separating the cavity pretreatment layer and the second intermediate layer comprises: heating the second intermediate layer so that the second intermediate layer loses its viscosity, thereby separating the cavity pretreatment layer and the second intermediate layer.

[0021] In some embodiments, the forming of the second layer further comprises: forming a second intermediate layer, which is located on the second substrate. In some embodiments, the material of the second intermediate layer includes, but is not limited to, a chemical with low surface energy. In some embodiments, the chemical with low surface energy includes, but is not limited to, at least one of the following: 1H, 1H, 2H, 2H-perfluoroheptadecanetrimethyloxysilane, polydimethylsiloxane, hydrocarbons, fluorocarbons, polyethylene, polypropylene, polytetrafluoroethylene. In some embodiments, joining the first layer and the second layer comprises: bonding the first intermediate layer and the second intermediate layer. In some embodiments, bonding the first intermediate layer and the second intermediate layer comprises: applying pressure to the first intermediate layer and the second intermediate layer so that the first intermediate layer and the second intermediate layer are bonded. In some embodiments, removing the second layer comprises: separating the first intermediate layer and the second intermediate layer, and removing the second intermediate layer and the second substrate. In some embodiments, separating the first intermediate layer and the second intermediate layer comprises: heating the second intermediate layer so that the second intermediate layer loses its viscosity, thereby separating the first intermediate layer and the second intermediate layer.

[0022] In some embodiments, the formation of the cavity pretreatment layer also includes: before the formation of the first intermediate layer, forming an etching shield layer, which is located on the piezoelectric layer and at least covers the sacrificial layer. In some embodiments, the material of the etching shield layer includes but is not limited to at least one of the following: aluminum nitride, silicon carbide, diamond, silicon nitride, silicon dioxide, aluminum oxide, titanium dioxide. In some embodiments, the thickness of the etching shield layer includes but is not limited to: 2 microns to 6 microns. It should be noted that when etching to form the cavity, the etching shield layer can protect the first intermediate layer. In addition, the etching shield layer can protect the resonant device from corrosion by water and oxygen.

[0023] In some embodiments, the forming of the piezoelectric layer includes: forming a first sub-piezoelectric layer, which is located on the first substrate; forming a second sub-piezoelectric layer, which is located on the first sub-piezoelectric layer. In some embodiments, the half-peak width of the rocking curve of the first sub-piezoelectric layer is higher than 1.7 degrees; the half-peak width of the rocking curve of the second sub-piezoelectric layer is lower than 1.7 degrees. In some embodiments, the method for forming the resonant device further includes: after removing the first substrate, removing the first sub-piezoelectric layer, and the first side corresponds to the second piezoelectric layer side. It should be noted that the half-peak width of the rocking curve lower than 1.7 degrees indicates good lattice quality, and higher than 1.7 degrees indicates poor lattice quality. When the first substrate is removed, the lattice quality of the piezoelectric layer will be affected. Therefore, by using the above-mentioned piezoelectric layer comprising a two-layer structure, after removing the first substrate, the first sub-piezoelectric layer of poor quality is removed, leaving the second sub-piezoelectric layer of good quality, thereby further improving the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0024] In some embodiments, the forming of the first layer further comprises: before forming the piezoelectric layer, forming a photolithographic mark. In some embodiments, the forming of the photolithographic mark comprises: forming an opening at one end of the first substrate; forming the photolithographic mark to be located in the opening. In some embodiments, the method for forming the resonant device further comprises: after removing the first substrate, retaining the photolithographic mark to be located on the first side and contacting the piezoelectric layer.

[0025] In some embodiments, the method for forming the resonant device further includes: before forming the second electrode layer, forming an edge structure, which is located on the first side and contacts the piezoelectric layer. In some embodiments, the forming of the second electrode layer includes: forming the second electrode layer, which is located on the inner side of the edge structure. It should be noted that the edge structure is located outside the edge of the second electrode layer, forming a surrounding edge of the second electrode layer, which is used to limit the leakage of lateral waves, thereby improving the Q value of the resonant device. In addition, the edge structure is located in the resonance zone. In some embodiments, the edge structure is a ring-shaped structure.

[0026] In some embodiments, the forming of the edge structure includes but is not limited to: forming a metal edge structure, located on the first side, contacting the piezoelectric layer. In some embodiments, the forming of the edge structure also includes: etching the inner side of the metal edge structure (i.e., the inner side of the edge structure) to form a slope. In some embodiments, the etching angle of the inner side of the metal edge structure includes but is not limited to: 1 degree to 89 degrees. It should be noted that the formation of a slope on the inner side of the edge structure and the keeping of a straight surface on the outer side can increase the impedance of the edge structure, thereby better limiting the leakage of lateral waves.

[0027] It should be noted that the photolithography mark has a calibration function, and the edge structure or the second electrode layer is formed by aligning with the photolithography mark to improve the accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1a is a schematic diagram of a bulk acoustic wave filter circuit;

[0029] Figure 1b is a schematic diagram of a cross-sectional structure of a FBAR 100;

[0030] Figure 2 is a schematic flow chart of a method 200 for forming a bulk acoustic wave resonator device according to an embodiment of the present invention;

[0031] Figure 3a It is a schematic flow chart of a method 300a for forming a cavity pretreatment layer in a method 200 for forming a bulk acoustic wave resonator device according to an embodiment of the present invention;

[0032] Figure 3b It is a schematic flow chart of a method 300b for forming a cavity pretreatment layer in a method 200 for forming a bulk acoustic wave resonator device according to an embodiment of the present invention;

[0033] Figure 3c It is a schematic flow chart of a method 300c for forming a cavity pretreatment layer in a method 200 for forming a bulk acoustic wave resonator device according to an embodiment of the present invention;

[0034] Figures 4 to 8 is a schematic cross-sectional structural diagram of a method for forming a bulk acoustic wave resonance device according to an embodiment of the present invention;

[0035] Figures 9 to 12 is a schematic cross-sectional structural diagram of a method for forming a bulk acoustic wave resonance device according to an embodiment of the present invention;

[0036] Figures 13 to 16 is a schematic cross-sectional structural diagram of a method for forming a bulk acoustic wave resonance device according to an embodiment of the present invention;

[0037] Fig.17 It is a schematic diagram of the structure of a hexagonal crystal;

[0038] Fig.18 (i) is a schematic diagram of the structure of an orthorhombic crystal;

[0039] Fig.18 (ii) is a schematic diagram of the structure of a tetragonal crystal;

[0040] Fig.18 (iii) is a schematic diagram of the structure of a cubic crystal. DETAILED DESCRIPTION

[0041] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0042] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0043] As mentioned in the background section, see Figure 1b, the FBAR 100 is formed by stacking layer by layer, that is, the electrode layer 107 is formed on the substrate 101, the piezoelectric layer 105 is formed on the electrode layer 107, and then the electrode layer 109 is formed on the piezoelectric layer 105. Since the electrode layer 107 is convex, directly forming the piezoelectric layer 105 on the electrode layer 107 will cause some crystals in the piezoelectric layer 105 (for example, crystals at both side edges of the piezoelectric layer 105 in the horizontal direction) to turn significantly and not be parallel to other crystals, thereby reducing the electromechanical coupling coefficient and Q value of the FBAR. In addition, the substrate 101 will cause electrical loss.

[0044] The inventors of the present invention have found that by forming a piezoelectric layer on a first substrate, since the surface of the first substrate is flat, the piezoelectric layer can include no obvious turned crystals, thereby helping to improve the electromechanical coupling coefficient and Q value of the resonant device.

[0045] The inventors of the present invention have also found that removing the second substrate can eliminate the electrical loss caused by the second substrate.

[0046] Furthermore, due to the lattice mismatch between the material of the first substrate and the material of the piezoelectric layer, the piezoelectric layer is divided into two sub-piezoelectric layers based on different lattice qualities, wherein the first sub-piezoelectric layer is a transition layer between the first substrate and the second sub-piezoelectric layer, and has a poor lattice quality, and the second sub-piezoelectric layer is formed on the first sub-piezoelectric layer, and has a good lattice quality. If the first sub-piezoelectric layer with poor lattice quality cannot be removed, the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device will be affected. It should be noted that, see Figure 1b The FBAR 100 is formed by stacking layer by layer, and the piezoelectric layer 105 is directly formed on the electrode layer 107, so the sub-piezoelectric layer contacting the electrode layer 107 with poor lattice quality cannot be removed.

[0047] The inventors of the present invention have found that after removing the first substrate, the first sub-piezoelectric layer with poor lattice quality can be further removed, leaving the second sub-piezoelectric layer with better lattice quality, thereby further improving the electromechanical coupling coefficient of the resonance device and the Q value of the resonance device.

[0048] The inventors of the present invention have also found that the photolithographic marks on the piezoelectric layer have a calibration function, and the edge structure or the upper electrode layer is aligned relative to the photolithographic marks to improve the accuracy.

[0049] Figure 2 2 is a flow chart of a method 200 for forming a bulk acoustic wave resonator device according to an embodiment of the present invention.

[0050] like Figure 2As shown, an embodiment of the present invention provides a method 200 for forming a bulk acoustic wave resonator device, comprising:

[0051] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer contacts the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0052] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0053] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0054] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0055] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0056] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0057] Step S213, removing the second layer.

[0058] It should be noted that the piezoelectric layer is formed on the first substrate. Since the surface of the first substrate is flat, the piezoelectric layer does not include crystals with obvious turning, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device. In addition, removing the second substrate can eliminate the electrical loss caused by the second substrate.

[0059] In this embodiment, the material of the first substrate includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0060] In this embodiment, the material of the piezoelectric layer includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

[0061] In this embodiment, the piezoelectric layer includes a plurality of crystals, and the plurality of crystals include a first crystal and a second crystal, wherein the first crystal and the second crystal are any two crystals of the plurality of crystals. A person skilled in the art knows that the crystal orientation, crystal plane, etc. of a crystal can be represented based on a coordinate system. Fig.17 As shown in FIG. 1 , for a hexagonal crystal, such as aluminum nitride crystal, an ac stereo coordinate system (including an a-axis and a c-axis) is used to represent it. Fig.18 As shown, for crystals of (i) orthorhombic system (a≠b≠c), (ii) tetragonal system (a=b≠c), (iii) cubic system (a=b=c), etc., an xyz three-dimensional coordinate system (including x-axis, y-axis and z-axis) is used for representation. In addition to the above two examples, crystals can also be represented based on other coordinate systems known to those skilled in the art, so the present invention is not limited to the above two examples.

[0062] In an embodiment of the present invention, the first crystal can be represented based on a first three-dimensional coordinate system, and the second crystal can be represented based on a second three-dimensional coordinate system, wherein the first three-dimensional coordinate system at least includes a first coordinate axis along a first direction and a third coordinate axis along a third direction, and the second three-dimensional coordinate system at least includes a second coordinate axis along a second direction and a fourth coordinate axis along a fourth direction, wherein the first coordinate axis corresponds to the height of the first crystal, and the second coordinate axis corresponds to the height of the second crystal.

[0063] In the embodiment of the present invention, the first direction and the second direction are the same or opposite. It should be noted that the first direction and the second direction are the same means that the angle between the vector along the first direction and the vector along the second direction ranges from 0 degrees to 5 degrees; the first direction and the second direction are opposite means that the angle between the vector along the first direction and the vector along the second direction ranges from 175 degrees to 180 degrees.

[0064] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the first coordinate axis is the first c-axis, and the third coordinate axis is the first a-axis; the second three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, wherein the first c-axis and the second c-axis point in the same or opposite directions.

[0065] In another embodiment, the first three-dimensional coordinate system further includes a fifth coordinate axis along a fifth direction, and the second three-dimensional coordinate system further includes a sixth coordinate axis along a sixth direction. In another embodiment, the first direction is the same as or opposite to the second direction, and the third direction is the same as or opposite to the fourth direction. It should be noted that the third direction is the same as the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 0 degrees to 5 degrees; the third direction is opposite to the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 175 degrees to 180 degrees.

[0066] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the first coordinate axis is the first z-axis, the third coordinate axis is the first y-axis, and the fifth coordinate axis is the first x-axis; the second three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the second coordinate axis is the second z-axis, the fourth coordinate axis is the second y-axis, and the sixth coordinate axis is the second x-axis. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in the same direction. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in the same direction.

[0067] In this embodiment, the piezoelectric layer includes a plurality of crystals, and the half-peak width of the rocking curve of the plurality of crystals is less than 2.5 degrees. It should be noted that the rocking curve describes the angular divergence of a certain crystal plane (the crystal plane determined by the diffraction angle) in the sample, and is represented by a plane coordinate system, wherein the horizontal axis is the angle between the crystal plane and the sample plane, and the vertical axis represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the lattice quality, and the smaller the half-peak width angle, the better the lattice quality. In addition, the full width at half maximum (FWHM) refers to the distance between the two points where the function value is equal to half of the peak value in a peak of the function.

[0068] In this embodiment, the material of the second substrate includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0069] In this embodiment, step S205 includes: bonding the cavity pretreatment layer to the second substrate. In another embodiment, bonding the cavity pretreatment layer to the second substrate includes: applying pressure to the cavity pretreatment layer and the second substrate to bond the cavity pretreatment layer to the second substrate.

[0070] In this embodiment, the materials of the first electrode layer and the second electrode layer include but are not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0071] In this embodiment, in step S211, the etching method includes but is not limited to at least one of the following: oxygen ion etching, hydrofluoric acid etching, and xenon difluoride etching.

[0072] In this embodiment, step S213 includes: removing the second substrate by grinding.

[0073] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0074] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer contacts the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0075] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0076] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0077] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0078] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0079] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0080] Step S213, removing the second layer.

[0081] In this embodiment, Figure 3a As shown, the forming of the cavity pretreatment layer in step S201 includes:

[0082] Step S2011, forming a sacrificial layer, which is located on the piezoelectric layer and covers the first end;

[0083] Step S2013, forming an etching shielding layer, which is located on the piezoelectric layer and covers the sacrificial layer and the second end of the first electrode layer;

[0084] Step S2015, forming a first intermediate layer located on the etching shield layer, so that the second side corresponds to the first intermediate layer side, wherein the etching shield layer is located between the first intermediate layer and the piezoelectric layer.

[0085] In this embodiment, the material of the sacrificial layer includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, polysilicon. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (ie, BCB), photosensitive epoxy resin photoresist (eg, SU-8), polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0086] In this embodiment, the material of the etching shield layer includes but is not limited to at least one of the following: aluminum nitride, silicon carbide, diamond, silicon nitride, silicon dioxide, aluminum oxide, titanium dioxide. In this embodiment, the thickness of the etching shield layer includes but is not limited to: 2 microns to 6 microns.

[0087] In this embodiment, the material of the first intermediate layer includes but is not limited to at least one of the following: polymer, insulating dielectric. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes but is not limited to at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide. In this embodiment, the thickness of the first intermediate layer includes but is not limited to: 20 microns to 100 microns. It should be noted that the acoustic impedance of the first intermediate layer can be small.

[0088] In this embodiment, step S205 includes: bonding the first intermediate layer and the second substrate. In another embodiment, bonding the first intermediate layer and the second substrate includes: applying pressure to the first intermediate layer and the second substrate to bond the first intermediate layer and the second substrate.

[0089] In this embodiment, step S211 includes: etching to remove the sacrificial layer to form the cavity, wherein the first end is located in the cavity. In this embodiment, the etching method includes but is not limited to at least one of the following: oxygen ion etching, hydrofluoric acid etching, and xenon difluoride etching. It should be noted that the etching shielding layer can protect the first intermediate layer when etching to form the cavity. In addition, the etching shielding layer can protect the resonant device from corrosion by water and oxygen.

[0090] In this embodiment, step S213 includes: removing the second substrate by grinding.

[0091] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0092] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer contacts the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0093] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0094] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0095] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0096] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0097] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0098] Step S213, removing the second layer.

[0099] In this embodiment, Figure 3b As shown, the forming of the cavity pretreatment layer in step S201 includes:

[0100] Step S2011', forming a sacrificial layer, which is located on the piezoelectric layer and covers the first end;

[0101] Step S2013', forming an etching shielding layer, which is located on the piezoelectric layer and covers the sacrificial layer and the second end of the first electrode layer;

[0102] Step S2015', forming a first intermediate layer, which is located on the piezoelectric layer, covers the etching shield layer, and contacts the piezoelectric layer, so that the second side corresponds to the first intermediate layer side.

[0103] In this embodiment, the material of the sacrificial layer includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, polysilicon. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (ie, BCB), photosensitive epoxy resin photoresist (eg, SU-8), polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0104] In this embodiment, the material of the etching shield layer includes but is not limited to at least one of the following: aluminum nitride, silicon carbide, diamond, silicon nitride, silicon dioxide, aluminum oxide, titanium dioxide. In this embodiment, the thickness of the etching shield layer includes but is not limited to: 2 microns to 6 microns.

[0105] In this embodiment, the material of the first intermediate layer includes but is not limited to at least one of the following: polymer, insulating dielectric. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes but is not limited to at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide. In this embodiment, the thickness of the first intermediate layer includes but is not limited to: 20 microns to 100 microns. It should be noted that the acoustic impedance of the first intermediate layer can be small.

[0106] In this embodiment, step S205 includes: bonding the first intermediate layer and the second substrate. In another embodiment, bonding the first intermediate layer and the second substrate includes: applying pressure to the first intermediate layer and the second substrate to bond the first intermediate layer and the second substrate.

[0107] In this embodiment, step S211 includes: etching to remove the sacrificial layer to form the cavity, wherein the first end is located in the cavity. In this embodiment, the etching method includes but is not limited to at least one of the following: oxygen ion etching, hydrofluoric acid etching, and xenon difluoride etching. It should be noted that the etching shielding layer can protect the first intermediate layer when etching to form the cavity. In addition, the etching shielding layer can protect the resonant device from corrosion by water and oxygen.

[0108] In this embodiment, step S213 includes: removing the second substrate by grinding.

[0109] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0110] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer is in contact with the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0111] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0112] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0113] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0114] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0115] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0116] Step S213, removing the second layer.

[0117] In this embodiment, Figure 3c As shown, the forming of the cavity pretreatment layer in step S201 includes:

[0118] Step S2011', forming a sacrificial layer on the piezoelectric layer and covering the first end;

[0119] Step S2013', forming an etching shielding layer, which is located on the piezoelectric layer and covers the sacrificial layer;

[0120] Step S2015', forming a first intermediate layer, which is located on the piezoelectric layer, covers the etching shield layer and the second end of the first electrode layer, and contacts the piezoelectric layer, so that the second side corresponds to the first intermediate layer side.

[0121] In this embodiment, the material of the sacrificial layer includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, polysilicon. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (ie, BCB), photosensitive epoxy resin photoresist (eg, SU-8), polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0122] In this embodiment, the material of the etching shield layer includes but is not limited to at least one of the following: aluminum nitride, silicon carbide, diamond, silicon nitride, silicon dioxide, aluminum oxide, titanium dioxide. In this embodiment, the thickness of the etching shield layer includes but is not limited to: 2 microns to 6 microns.

[0123] In this embodiment, the material of the first intermediate layer includes but is not limited to at least one of the following: polymer, insulating dielectric. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes but is not limited to at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide. In this embodiment, the thickness of the first intermediate layer includes but is not limited to: 20 microns to 100 microns. It should be noted that the acoustic impedance of the first intermediate layer can be small.

[0124] In this embodiment, step S205 includes: bonding the first intermediate layer and the second substrate. In another embodiment, bonding the first intermediate layer and the second substrate includes: applying pressure to the first intermediate layer and the second substrate to bond the first intermediate layer and the second substrate.

[0125] In this embodiment, step S211 includes: etching to remove the sacrificial layer to form the cavity, wherein the first end is located in the cavity. In this embodiment, the etching method includes but is not limited to at least one of the following: oxygen ion etching, hydrofluoric acid etching, and xenon difluoride etching. It should be noted that the etching shielding layer can protect the first intermediate layer when etching to form the cavity. In addition, the etching shielding layer can protect the resonant device from corrosion by water and oxygen.

[0126] In this embodiment, step S213 includes: removing the second substrate by grinding.

[0127] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0128] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer is in contact with the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0129] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0130] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0131] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0132] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0133] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0134] Step S213, removing the second layer.

[0135] In this embodiment, step S203 further includes: forming a second intermediate layer located on the second substrate.

[0136] In this embodiment, the material of the second intermediate layer includes but is not limited to: low surface energy chemical substances. In this embodiment, the low surface energy chemical substances include but are not limited to at least one of the following: 1H, 1H, 2H, 2H-perfluoroheptadecanetrimethyloxysilane, polydimethylsiloxane, hydrocarbons, fluorocarbons, polyethylene, polypropylene, polytetrafluoroethylene.

[0137] In this embodiment, step S205 includes: bonding the cavity pretreatment layer and the second intermediate layer. In another embodiment, bonding the cavity pretreatment layer and the second intermediate layer includes: applying pressure to the cavity pretreatment layer and the second intermediate layer to bond the cavity pretreatment layer and the second intermediate layer.

[0138] In this embodiment, step S213 includes: separating the cavity pretreatment layer and the second intermediate layer to remove the second layer. In another embodiment, separating the cavity pretreatment layer and the second intermediate layer includes: heating the second intermediate layer to make the second intermediate layer lose viscosity, thereby separating the cavity pretreatment layer and the second intermediate layer.

[0139] It should be noted that the second intermediate layer made of low surface energy material is helpful to easily remove the second substrate and can better protect the second substrate so that the second substrate can be reused, thereby reducing production costs.

[0140] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0141] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer is in contact with the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0142] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0143] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0144] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0145] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0146] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0147] Step S213, removing the second layer.

[0148] In this embodiment, the forming of the cavity pretreatment layer in step S201 includes:

[0149] forming a sacrificial layer, located on the piezoelectric layer and covering the first end;

[0150] A first intermediate layer is formed on the piezoelectric layer, covers the sacrificial layer and the second end of the first electrode layer, and contacts the piezoelectric layer, so that the second side corresponds to the first intermediate layer side.

[0151] In this embodiment, the material of the sacrificial layer includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, polysilicon. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (ie, BCB), photosensitive epoxy resin photoresist (eg, SU-8), polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0152] In this embodiment, the material of the first intermediate layer includes but is not limited to at least one of the following: polymer, insulating dielectric. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes but is not limited to at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide. In this embodiment, the thickness of the first intermediate layer includes but is not limited to: 20 microns to 100 microns. It should be noted that the acoustic impedance of the first intermediate layer can be small.

[0153] In this embodiment, step S203 further includes: forming a second intermediate layer located on the second substrate.

[0154] In this embodiment, the material of the second intermediate layer includes but is not limited to: low surface energy chemical substances. In this embodiment, the low surface energy chemical substances include but are not limited to at least one of the following: 1H, 1H, 2H, 2H-perfluoroheptadecanetrimethyloxysilane, polydimethylsiloxane, hydrocarbons, fluorocarbons, polyethylene, polypropylene, polytetrafluoroethylene.

[0155] In this embodiment, step S205 includes: bonding the first intermediate layer and the second intermediate layer. In another embodiment, bonding the first intermediate layer and the second intermediate layer includes: applying pressure to the first intermediate layer and the second intermediate layer to bond the first intermediate layer and the second intermediate layer.

[0156] In this embodiment, step S211 includes: etching to remove the sacrificial layer to form the cavity, wherein the first end is located in the cavity. In this embodiment, the etching method includes but is not limited to at least one of the following: oxygen ion etching, hydrofluoric acid etching, and xenon difluoride etching.

[0157] In this embodiment, step S213 includes: separating the first intermediate layer and the second intermediate layer to remove the second layer. In another embodiment, separating the first intermediate layer and the second intermediate layer includes: heating the second intermediate layer to make the second intermediate layer lose viscosity, thereby separating the first intermediate layer and the second intermediate layer.

[0158] It should be noted that the second intermediate layer made of low surface energy material is helpful to easily remove the second substrate and can better protect the second substrate so that the second substrate can be reused, thereby reducing production costs.

[0159] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0160] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer is in contact with the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0161] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0162] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0163] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0164] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0165] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0166] Step S213, removing the second layer.

[0167] In this embodiment, the forming of the piezoelectric layer in step S201 includes: forming a first sub-piezoelectric layer located on the first substrate; and forming a second sub-piezoelectric layer located on the first sub-piezoelectric layer.

[0168] In this embodiment, the half-peak width of the rocking curve of the first sub-piezoelectric layer is higher than 1.7 degrees, and the half-peak width of the rocking curve of the second sub-piezoelectric layer is lower than 1.7 degrees. It should be noted that the rocking curve describes the angular divergence of a specific crystal plane (the crystal plane determined by the diffraction angle) in the sample, and is represented by a plane coordinate system, wherein the horizontal axis is the angle between the crystal plane and the sample plane, and the vertical axis represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the lattice quality. The smaller the half-peak width angle, the better the lattice quality (that is, the half-peak width of the rocking curve is lower than 1.7 degrees for good lattice quality, and higher than 1.7 degrees for poor lattice quality). In addition, the full width at half maximum (FWHM) refers to the distance between the two points where the function value is equal to half of the peak value in a peak of the function.

[0169] In this embodiment, the material of the first sub-piezoelectric layer includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the second sub-piezoelectric layer includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the first sub-piezoelectric layer is the same as the material of the second sub-piezoelectric layer. In another embodiment, the material of the first sub-piezoelectric layer may be different from the material of the second sub-piezoelectric layer.

[0170] In this embodiment, the second sub-piezoelectric layer includes a plurality of crystals, the plurality of crystals include a first crystal and a second crystal, wherein the first crystal and the second crystal are any two crystals of the plurality of crystals. A person skilled in the art knows that the crystal orientation, crystal plane, etc. of a crystal can be represented based on a coordinate system. Fig.17 As shown in FIG. 1 , for a hexagonal crystal, such as aluminum nitride crystal, an ac stereo coordinate system (including an a-axis and a c-axis) is used to represent it. Fig.18 As shown, for crystals of (i) orthorhombic system (a≠b≠c), (ii) tetragonal system (a=b≠c), (iii) cubic system (a=b=c), etc., an xyz three-dimensional coordinate system (including x-axis, y-axis and z-axis) is used for representation. In addition to the above two examples, crystals can also be represented based on other coordinate systems known to those skilled in the art, so the present invention is not limited to the above two examples.

[0171] In this embodiment, the first crystal can be represented based on a first three-dimensional coordinate system, and the second crystal can be represented based on a second three-dimensional coordinate system, wherein the first three-dimensional coordinate system at least includes a first coordinate axis along a first direction and a third coordinate axis along a third direction, and the second three-dimensional coordinate system at least includes a second coordinate axis along a second direction and a fourth coordinate axis along a fourth direction, wherein the first coordinate axis corresponds to the height of the first crystal, and the second coordinate axis corresponds to the height of the second crystal.

[0172] In this embodiment, the first direction and the second direction are the same or opposite. It should be noted that the first direction and the second direction are the same means that the angle between the vector along the first direction and the vector along the second direction ranges from 0 degrees to 5 degrees; the first direction and the second direction are opposite means that the angle between the vector along the first direction and the vector along the second direction ranges from 175 degrees to 180 degrees.

[0173] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the first coordinate axis is the first c-axis, and the third coordinate axis is the first a-axis; the second three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, wherein the first c-axis and the second c-axis point in the same or opposite directions.

[0174] In another embodiment, the first three-dimensional coordinate system further includes a fifth coordinate axis along a fifth direction, and the second three-dimensional coordinate system further includes a sixth coordinate axis along a sixth direction. In another embodiment, the first direction is the same as or opposite to the second direction, and the third direction is the same as or opposite to the fourth direction. It should be noted that the third direction is the same as the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 0 degrees to 5 degrees; the third direction is opposite to the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 175 degrees to 180 degrees.

[0175] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the first coordinate axis is the first z-axis, the third coordinate axis is the first y-axis, and the fifth coordinate axis is the first x-axis; the second three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the second coordinate axis is the second z-axis, the fourth coordinate axis is the second y-axis, and the sixth coordinate axis is the second x-axis. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in the same direction. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in the same direction.

[0176] In this embodiment, the method 200 for forming the resonant device further includes: after step S207, removing the first sub-piezoelectric layer, so that the first side corresponds to the second sub-piezoelectric layer side.

[0177] In this embodiment, step S209 includes: forming the second electrode layer contacting the second sub-piezoelectric layer.

[0178] It should be noted that the lattice of the material of the first substrate and the material of the piezoelectric layer do not match. Based on different lattice qualities, the piezoelectric layer is divided into two sub-piezoelectric layers, wherein the first sub-piezoelectric layer is a transition layer between the first substrate and the second sub-piezoelectric layer, and has a poor lattice quality; the second sub-piezoelectric layer is formed on the first sub-piezoelectric layer, and has a good lattice quality. In this embodiment, after removing the first substrate, the first sub-piezoelectric layer with poor lattice quality is further removed, leaving the second sub-piezoelectric layer with good lattice quality, thereby further improving the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0179] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0180] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer is in contact with the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0181] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0182] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0183] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0184] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0185] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0186] Step S213, removing the second layer.

[0187] In this embodiment, step S201 further includes: before forming the piezoelectric layer, forming a photolithography mark. In this embodiment, forming the photolithography mark includes: forming an opening on one end of the first substrate; and forming the photolithography mark in the opening.

[0188] In this embodiment, the material of the photolithographic mark includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the piezoelectric layer includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the photolithographic mark is the same as the material of the piezoelectric layer. In another embodiment, the material of the photolithographic mark may be different from the material of the piezoelectric layer.

[0189] In this embodiment, step S207 further includes: retaining the photolithography mark located at one end of the piezoelectric layer, wherein the photolithography mark is located at the first side and contacts the piezoelectric layer.

[0190] In this embodiment, step S209 includes: forming the second electrode layer based on the photolithography mark.

[0191] It should be noted that the photolithography mark has a calibration function, and the second electrode layer is aligned relative to the photolithography mark to improve the accuracy.

[0192] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0193] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0194] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0195] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0196] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0197] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0198] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0199] Step S213, removing the second layer.

[0200] In this embodiment, step S201 further includes: before forming the piezoelectric layer, forming a photolithography mark. In this embodiment, forming the photolithography mark includes: forming an opening on one end of the first substrate; and forming the photolithography mark in the opening.

[0201] In this embodiment, the material of the photolithography mark includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

[0202] In this embodiment, the forming of the piezoelectric layer in step S201 includes: forming a first sub-piezoelectric layer located on the first substrate and the photolithography mark; and forming a second sub-piezoelectric layer located on the first sub-piezoelectric layer.

[0203] In this embodiment, the half-peak width of the rocking curve of the first sub-piezoelectric layer is higher than 1.7 degrees, and the half-peak width of the rocking curve of the second sub-piezoelectric layer is lower than 1.7 degrees. It should be noted that the rocking curve describes the angular divergence of a specific crystal plane (the crystal plane determined by the diffraction angle) in the sample, and is represented by a plane coordinate system, wherein the horizontal axis is the angle between the crystal plane and the sample plane, and the vertical axis represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the lattice quality. The smaller the half-peak width angle, the better the lattice quality (that is, the half-peak width of the rocking curve is lower than 1.7 degrees for good lattice quality, and higher than 1.7 degrees for poor lattice quality). In addition, the full width at half maximum (FWHM) refers to the distance between the two points where the function value is equal to half of the peak value in a peak of the function.

[0204] In this embodiment, the material of the first piezoelectric layer includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the second piezoelectric layer includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

[0205] In this embodiment, the material of the first piezoelectric sub-layer is the same as that of the second piezoelectric sub-layer. In another embodiment, the material of the first piezoelectric sub-layer is different from that of the second piezoelectric sub-layer. In this embodiment, the material of the photolithography mark is the same as that of the first piezoelectric sub-layer. In another embodiment, the material of the photolithography mark is different from that of the first piezoelectric sub-layer.

[0206] In this embodiment, the second sub-piezoelectric layer includes a plurality of crystals, the plurality of crystals include a first crystal and a second crystal, wherein the first crystal and the second crystal are any two crystals of the plurality of crystals. A person skilled in the art knows that the crystal orientation, crystal plane, etc. of a crystal can be represented based on a coordinate system. Fig.17 As shown in FIG. 1 , for a hexagonal crystal, such as aluminum nitride crystal, an ac stereo coordinate system (including an a-axis and a c-axis) is used to represent it. Fig.18 As shown, for crystals of (i) orthorhombic system (a≠b≠c), (ii) tetragonal system (a=b≠c), (iii) cubic system (a=b=c), etc., an xyz three-dimensional coordinate system (including x-axis, y-axis and z-axis) is used for representation. In addition to the above two examples, crystals can also be represented based on other coordinate systems known to those skilled in the art, so the present invention is not limited to the above two examples.

[0207] In this embodiment, the first crystal can be represented based on a first three-dimensional coordinate system, and the second crystal can be represented based on a second three-dimensional coordinate system, wherein the first three-dimensional coordinate system at least includes a first coordinate axis along a first direction and a third coordinate axis along a third direction, and the second three-dimensional coordinate system at least includes a second coordinate axis along a second direction and a fourth coordinate axis along a fourth direction, wherein the first coordinate axis corresponds to the height of the first crystal, and the second coordinate axis corresponds to the height of the second crystal.

[0208] In this embodiment, the first direction and the second direction are the same or opposite. It should be noted that the first direction and the second direction are the same means that the angle between the vector along the first direction and the vector along the second direction ranges from 0 degrees to 5 degrees; the first direction and the second direction are opposite means that the angle between the vector along the first direction and the vector along the second direction ranges from 175 degrees to 180 degrees.

[0209] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the first coordinate axis is the first c-axis, and the third coordinate axis is the first a-axis; the second three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, wherein the first c-axis and the second c-axis point in the same or opposite directions.

[0210] In another embodiment, the first three-dimensional coordinate system further includes a fifth coordinate axis along a fifth direction, and the second three-dimensional coordinate system further includes a sixth coordinate axis along a sixth direction. In another embodiment, the first direction is the same as or opposite to the second direction, and the third direction is the same as or opposite to the fourth direction. It should be noted that the third direction is the same as the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 0 degrees to 5 degrees; the third direction is opposite to the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 175 degrees to 180 degrees.

[0211] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the first coordinate axis is the first z-axis, the third coordinate axis is the first y-axis, and the fifth coordinate axis is the first x-axis; the second three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the second coordinate axis is the second z-axis, the fourth coordinate axis is the second y-axis, and the sixth coordinate axis is the second x-axis. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in the same direction. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in the same direction.

[0212] In this embodiment, the method 200 for forming the resonant device further includes: after step S207, removing the first sub-piezoelectric layer so that the first side corresponds to the second sub-piezoelectric layer side; retaining the photolithography mark located at one end of the second sub-piezoelectric layer, wherein the photolithography mark is located on the first side and contacts the second sub-piezoelectric layer.

[0213] In this embodiment, step S209 includes: forming the second electrode layer based on the photolithography mark, contacting the second sub-piezoelectric layer.

[0214] It should be noted that the lattice of the material of the first substrate and the material of the piezoelectric layer do not match. Based on different lattice qualities, the piezoelectric layer is divided into two sub-piezoelectric layers, wherein the first sub-piezoelectric layer is a transition layer between the first substrate and the second sub-piezoelectric layer, and has a poor lattice quality; the second sub-piezoelectric layer is formed on the first sub-piezoelectric layer, and has a good lattice quality. In this embodiment, after removing the first substrate, the first sub-piezoelectric layer with poor lattice quality is further removed, leaving the second sub-piezoelectric layer with good lattice quality, thereby further improving the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0215] In addition, the photolithography mark has a calibration function, and the second electrode layer is formed by aligning it relative to the photolithography mark, which can improve the accuracy.

[0216] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0217] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer is in contact with the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0218] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0219] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0220] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0221] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0222] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0223] Step S213, removing the second layer.

[0224] In this embodiment, the method 200 for forming the resonant device further includes: before step S209, forming an edge structure located at the first side and contacting the piezoelectric layer. In this embodiment, the edge structure is a ring structure.

[0225] In this embodiment, the forming edge structure includes: forming a metal edge structure, located on the first side, contacting the piezoelectric layer. In another embodiment, the forming edge structure includes: forming a polymer edge structure, located on the first side, contacting the piezoelectric layer; forming a metal edge structure, located on the polymer edge structure.

[0226] In this embodiment, the forming of the edge structure further comprises: etching the inner side of the metal edge structure (ie, the inner side of the edge structure) to form a slope. In this embodiment, the etching angle of etching the inner side of the metal edge structure includes but is not limited to: 1 degree to 89 degrees.

[0227] In this embodiment, step S209 includes: forming the second electrode layer located inside the edge structure.

[0228] It should be noted that the edge structure is located outside the edge of the second electrode layer, forming a surrounding edge of the second electrode layer, which is used to limit the leakage of transverse waves, thereby improving the Q value of the resonant device. In addition, the edge structure is located in the resonance zone, wherein the resonance zone at least includes the piezoelectric layer, the first electrode layer, the edge structure and the second electrode layer. In addition, the inner side of the edge structure forms a slope surface, and the outer side remains a straight surface, which can increase the impedance of the edge structure, thereby better limiting the leakage of transverse waves.

[0229] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0230] Step S201, forming a first layer, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers a first end of the first electrode layer, and the cavity pretreatment layer is in contact with the piezoelectric layer, wherein a first side of the first layer corresponds to a side of the first substrate, and a second side of the first layer corresponds to a side of the cavity pretreatment layer (i.e., the first side is opposite to the second side);

[0231] Step S203, forming a second layer, wherein forming the second layer includes: providing a second substrate;

[0232] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0233] Step S207, removing the first substrate so that the first side corresponds to the piezoelectric layer side;

[0234] Step S209, forming a second electrode layer, wherein the second electrode layer is located on the first side and contacts the piezoelectric layer;

[0235] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity; and

[0236] Step S213, removing the second layer.

[0237] In this embodiment, step S201 further includes: before forming the piezoelectric layer, forming a photolithography mark. In this embodiment, forming the photolithography mark includes: forming an opening on one end of the first substrate; and forming the photolithography mark in the opening.

[0238] In this embodiment, the material of the photolithographic mark includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the piezoelectric layer includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the photolithographic mark is the same as the material of the piezoelectric layer. In another embodiment, the material of the photolithographic mark may be different from the material of the piezoelectric layer.

[0239] In this embodiment, step S207 further includes: retaining the photolithography mark located at one end of the piezoelectric layer, wherein the photolithography mark is located at the first side and contacts the piezoelectric layer.

[0240] In this embodiment, the method 200 for forming the resonant device further includes: before step S209, based on the photolithography mark, forming an edge structure located at the first side and contacting the piezoelectric layer. In this embodiment, the edge structure is a ring structure.

[0241] In this embodiment, the forming edge structure includes: forming a metal edge structure based on the photolithography mark, located on the first side and contacting the piezoelectric layer. In another embodiment, the forming edge structure includes: forming a polymer edge structure based on the photolithography mark, located on the first side and contacting the piezoelectric layer; forming a metal edge structure located on the polymer edge structure.

[0242] In this embodiment, the forming of the edge structure further comprises: etching the inner side of the metal edge structure (ie, the inner side of the edge structure) to form a slope. In this embodiment, the etching angle of etching the inner side of the metal edge structure includes but is not limited to: 1 degree to 89 degrees.

[0243] In this embodiment, step S209 includes: based on the photolithography mark, forming the second electrode layer located inside the edge structure.

[0244] It should be noted that the photolithography mark has a calibration function, and the edge structure is formed and the second electrode layer is aligned relative to the photolithography mark, which can improve the accuracy.

[0245] In addition, the edge structure is located outside the edge of the second electrode layer, forming a surrounding edge of the second electrode layer, which is used to limit the leakage of transverse waves, thereby improving the Q value of the resonant device. In addition, the edge structure is located in the resonance region, wherein the resonance region at least includes the piezoelectric layer, the first electrode layer, the edge structure and the second electrode layer. In addition, the inner side of the edge structure forms a slope surface, and the outer side remains a straight surface, which can increase the impedance of the edge structure, thereby better limiting the leakage of transverse waves.

[0246] In conjunction with the cross-sectional structural diagram of the bulk acoustic wave resonance device, the embodiments of the present invention provide the following three specific methods for forming the bulk acoustic wave resonance device to facilitate a better understanding of the present invention. However, the present invention can also be implemented in other ways different from the following embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0247] Figures 4 to 8 It is a schematic structural diagram of cross-section A of a method for forming a bulk acoustic wave resonance device according to an embodiment of the present invention.

[0248] like Figure 4 As shown, the method for forming the resonant device includes: forming a first layer, wherein the forming the first layer includes:

[0249] Providing a substrate 401;

[0250] An opening 401a is formed at one end of the substrate 401;

[0251] Forming a photolithography mark 402 located in the opening 401a;

[0252] forming a sub-piezoelectric layer 403, which is located on the substrate 401 and the photolithography mark 402;

[0253] A sub-piezoelectric layer 405 is formed and located on the sub-piezoelectric layer 403 .

[0254] In this embodiment, the material of the substrate 401 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0255] In this embodiment, the material of the photolithography mark 402 includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the sub-piezoelectric layer 403 includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the photolithography mark 402 and the sub-piezoelectric layer 403 is the same. In another embodiment, the material of the photolithography mark 402 and the sub-piezoelectric layer 403 may be different.

[0256] In this embodiment, the material of the sub-piezoelectric layer 405 includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the sub-piezoelectric layer 403 is the same as that of the sub-piezoelectric layer 405. In another embodiment, the material of the sub-piezoelectric layer 403 and the sub-piezoelectric layer 405 may be different.

[0257] In this embodiment, the half-peak width of the rocking curve of the sub-piezoelectric layer 403 is higher than 1.7 degrees; the half-peak width of the rocking curve of the sub-piezoelectric layer 405 is lower than 1.7 degrees. It should be noted that the rocking curve describes the angular divergence of a specific crystal plane (the crystal plane determined by the diffraction angle) in the sample, and is represented by a plane coordinate system, wherein the horizontal axis is the angle between the crystal plane and the sample plane, and the vertical axis represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the lattice quality. The smaller the half-peak width angle, the better the lattice quality (that is, the half-peak width of the rocking curve is lower than 1.7 degrees for good lattice quality, and higher than 1.7 degrees for poor lattice quality). In addition, the full width at half maximum (FWHM) refers to the distance between the two points where the function value is equal to half of the peak value in a peak of the function.

[0258] It should be noted that the lattices of the material of the substrate 401 and the material of the piezoelectric layer do not match. Based on different lattice qualities, the piezoelectric layer is divided into two sub-piezoelectric layers, wherein the sub-piezoelectric layer 403 is a transition layer between the substrate 401 and the sub-piezoelectric layer 405, and has poor lattice quality; the sub-piezoelectric layer 405 is formed on the sub-piezoelectric layer 403, and has good lattice quality.

[0259] In this embodiment, the sub-piezoelectric layer 405 includes a plurality of crystals, and the plurality of crystals include a first crystal and a second crystal, wherein the first crystal and the second crystal are any two crystals of the plurality of crystals. A person skilled in the art knows that the crystal orientation, crystal plane, etc. of a crystal can be represented based on a coordinate system. Fig.17 As shown in FIG. 1 , for a hexagonal crystal, such as aluminum nitride crystal, an ac stereo coordinate system (including an a-axis and a c-axis) is used to represent it. Fig.18 As shown, for crystals of (i) orthorhombic system (a≠b≠c), (ii) tetragonal system (a=b≠c), (iii) cubic system (a=b=c), etc., an xyz three-dimensional coordinate system (including x-axis, y-axis and z-axis) is used for representation. In addition to the above two examples, crystals can also be represented based on other coordinate systems known to those skilled in the art, so the present invention is not limited to the above two examples.

[0260] In this embodiment, the first crystal can be represented based on a first three-dimensional coordinate system, and the second crystal can be represented based on a second three-dimensional coordinate system, wherein the first three-dimensional coordinate system at least includes a first coordinate axis along a first direction and a third coordinate axis along a third direction, and the second three-dimensional coordinate system at least includes a second coordinate axis along a second direction and a fourth coordinate axis along a fourth direction, wherein the first coordinate axis corresponds to the height of the first crystal, and the second coordinate axis corresponds to the height of the second crystal.

[0261] In this embodiment, the first direction and the second direction are the same or opposite. It should be noted that the first direction and the second direction are the same means that the angle between the vector along the first direction and the vector along the second direction ranges from 0 degrees to 5 degrees; the first direction and the second direction are opposite means that the angle between the vector along the first direction and the vector along the second direction ranges from 175 degrees to 180 degrees.

[0262] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the first coordinate axis is the first c-axis, and the third coordinate axis is the first a-axis; the second three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, wherein the first c-axis and the second c-axis point in the same or opposite directions.

[0263] In another embodiment, the first three-dimensional coordinate system further includes a fifth coordinate axis along a fifth direction, and the second three-dimensional coordinate system further includes a sixth coordinate axis along a sixth direction. In another embodiment, the first direction is the same as or opposite to the second direction, and the third direction is the same as or opposite to the fourth direction. It should be noted that the third direction is the same as the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 0 degrees to 5 degrees; the third direction is opposite to the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 175 degrees to 180 degrees.

[0264] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the first coordinate axis is the first z-axis, the third coordinate axis is the first y-axis, and the fifth coordinate axis is the first x-axis; the second three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the second coordinate axis is the second z-axis, the fourth coordinate axis is the second y-axis, and the sixth coordinate axis is the second x-axis. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in the same direction. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in the same direction.

[0265] In this embodiment, see Figure 5 , the forming of the first layer further comprises:

[0266] forming an electrode layer 501 located on the sub-piezoelectric layer 405, wherein the electrode layer 501 is located on a first side of the piezoelectric layer 405;

[0267] forming a sacrificial layer 503, which is located on the sub-piezoelectric layer 405 and covers the first end of the electrode layer 501;

[0268] forming an etching shielding layer 505 located on the sub-piezoelectric layer 405 and covering the sacrificial layer 503 and the second end of the electrode layer 501;

[0269] An intermediate layer 507 is formed and located on the etching shielding layer 505 , wherein the etching shielding layer 505 is located between the intermediate layer 507 and the sub-piezoelectric layer 405 .

[0270] In this embodiment, the material of the electrode layer 501 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0271] In this embodiment, the material of the sacrificial layer 503 includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, polysilicon. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (ie, BCB), photosensitive epoxy resin photoresist (eg, SU-8), polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0272] In this embodiment, the material of the etching shield layer 505 includes but is not limited to at least one of the following: aluminum nitride, silicon carbide, diamond, silicon nitride, silicon dioxide, aluminum oxide, titanium dioxide. In this embodiment, the thickness of the etching shield layer 505 includes but is not limited to: 2 microns to 6 microns.

[0273] In this embodiment, the material of the intermediate layer 507 includes but is not limited to at least one of the following: polymer, insulating dielectric. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes but is not limited to at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide. In this embodiment, the thickness of the intermediate layer 507 includes but is not limited to: 20 microns to 100 microns. It should be noted that the acoustic impedance of the intermediate layer 507 can be small.

[0274] In this embodiment, see Figure 6 The method for forming the resonant device further includes: forming a second layer, wherein the forming the second layer includes:

[0275] Providing a substrate 601;

[0276] An intermediate layer 603 is formed and located on the substrate 601 .

[0277] In this embodiment, the material of the substrate 601 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0278] In this embodiment, the material of the intermediate layer 603 includes but is not limited to: low surface energy chemical substances. In this embodiment, the low surface energy chemical substances include but are not limited to at least one of the following: 1H, 1H, 2H, 2H-perfluoroheptadecanetrimethyloxysilane, polydimethylsiloxane, hydrocarbons, fluorocarbons, polyethylene, polypropylene, polytetrafluoroethylene.

[0279] In this embodiment, reference Figure 7 , the method for forming the resonant device further comprises:

[0280] Bonding the intermediate layer 507 and the intermediate layer 603;

[0281] removing the substrate 401;

[0282] The sub-piezoelectric layer 403 is removed, and the photolithography mark 402 is retained and located at one end of the sub-piezoelectric layer 405, wherein the photolithography mark 402 is located at a second side of the sub-piezoelectric layer 405, and the second side is opposite to the first side of the sub-piezoelectric layer 405;

[0283] Based on the photolithography mark 402 , an edge structure 701 is formed, located on the second side and contacting the sub-piezoelectric layer 405 .

[0284] In this embodiment, bonding the intermediate layer 507 and the intermediate layer 603 includes: applying pressure to the intermediate layer 507 and the intermediate layer 603 to bond the intermediate layer 507 and the intermediate layer 603 .

[0285] In this embodiment, the edge structure 701 is a ring-shaped structure.

[0286] In this embodiment, the forming edge structure 701 includes: based on the photolithography mark 402, forming a metal edge structure, located on the second side, contacting the sub-piezoelectric layer 405. In another embodiment, the forming edge structure 701 includes: based on the photolithography mark 402, forming a polymer edge structure, located on the second side, contacting the sub-piezoelectric layer 405; forming a metal edge structure, located on the polymer edge structure.

[0287] In another embodiment, the forming edge structure 701 further comprises: etching the inner side of the metal edge structure (ie, the inner side of the edge structure 701) to form a slope. In another embodiment, the etching angle of the inner side of the metal edge structure includes but is not limited to: 1 degree to 89 degrees.

[0288] In this embodiment, the etching angle of the metal edge structure ranges from 30 degrees to 75 degrees.

[0289] It should be noted that after removing the substrate 401, further removing the sub-piezoelectric layer 403, leaving the sub-piezoelectric layer 405 with good lattice quality, can further improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0290] In this embodiment, reference Figure 8 , the method for forming the resonant device further comprises:

[0291] Based on the photolithography mark 402 , an electrode layer 801 is formed, which is located on the second side and contacts the sub-piezoelectric layer 405 , wherein the electrode layer 801 is located inside the edge structure 701 ;

[0292] The sacrificial layer 503 is removed by etching to form a cavity 803, wherein the first end of the electrode layer 501 is located in the cavity 803;

[0293] The intermediate layer 507 and the intermediate layer 603 are separated to remove the intermediate layer 603 and the substrate 601 , that is, to remove the second layer.

[0294] In this embodiment, the material of the electrode layer 801 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0295] In this embodiment, the etching method includes but is not limited to at least one of the following: oxygen ion etching, hydrofluoric acid etching, and xenon difluoride etching.

[0296] In this embodiment, separating the intermediate layer 507 and the intermediate layer 603 includes: heating the intermediate layer 603 to make the intermediate layer 603 lose its viscosity, thereby separating the intermediate layer 507 and the intermediate layer 603.

[0297] It should be noted that the photolithography mark 402 has a calibration function, and the edge structure 701 and the electrode layer 801 are aligned relative to the photolithography mark 402 to improve the accuracy.

[0298] In addition, the edge structure 701 is located outside the edge of the electrode layer 801 to form a surrounding edge of the electrode layer 801, which is used to limit the leakage of lateral waves, thereby improving the Q value of the resonance device.

[0299] In addition, the edge structure 701 is located in the resonance zone 805, wherein the resonance zone 805 at least includes the sub-piezoelectric layer 405, the electrode layer 501, the edge structure 701 and the electrode layer 801, and the resonance zone 805 is suspended relative to the cavity 803 and has no overlapping portion with the intermediate layer 507.

[0300] In addition, the inner side of the edge structure 701 forms a slope surface, while the outer side remains a straight surface, which can increase the impedance of the edge structure 701, thereby better limiting the leakage of lateral waves.

[0301] In addition, the etching shielding layer 505 can protect the intermediate layer 801 when the sacrificial layer 503 is etched away to form the cavity 803. In addition, the etching shielding layer 505 can protect the resonance device from being corroded by water and oxygen.

[0302] In addition, removing the substrate 601 can eliminate the electrical loss caused by the substrate 601 .

[0303] In addition, the intermediate layer 603 made of low surface energy material helps to easily remove the substrate 601 and can better protect the substrate 601 so that the substrate 601 can be reused, thereby reducing production costs.

[0304] In general, the main beneficial effects of this embodiment include:

[0305] (1) The sub-piezoelectric layer 403 and the sub-piezoelectric layer 405 are formed on the substrate 401. The surface of the substrate 401 is flat, so that the sub-piezoelectric layer 405 does not include crystals with obvious turning, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device;

[0306] (2) Removing the substrate 601 can eliminate the electrical loss caused by the substrate 601. In addition, the use of the intermediate layer 603 made of a low surface energy material facilitates the convenient removal of the substrate 601 and can better protect the substrate 601, so that the substrate 601 can be reused, thereby reducing production costs;

[0307] (3) After removing the substrate 401, further removing the sub-piezoelectric layer 403 with poor lattice quality, leaving the sub-piezoelectric layer 405 with good lattice quality, thereby further improving the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device;

[0308] (4) The photolithography mark 402 has a calibration function, and the edge structure 701 and the electrode layer 801 are aligned relative to the photolithography mark 402, which can improve the accuracy.

[0309] Figures 9 to 12 It is a schematic structural diagram of cross-section A of a method for forming a bulk acoustic wave resonance device according to an embodiment of the present invention.

[0310] like Fig. 9 As shown, an embodiment of the present invention provides a method for forming a bulk acoustic wave resonator device, including: forming a first layer, wherein the forming of the first layer includes:

[0311] Providing a substrate 901;

[0312] forming a piezoelectric layer 903 located on the substrate 901;

[0313] forming an electrode layer 905 located on the piezoelectric layer 903, wherein the electrode layer 905 is located on a first side of the piezoelectric layer 903;

[0314] forming the sacrificial layer 907, which is located on the piezoelectric layer 903 and covers the first end of the electrode layer 905;

[0315] forming the etching shielding layer 909, which is located on the piezoelectric layer 903 and covers the sacrificial layer 907;

[0316] An intermediate layer 911 is formed, located on the piezoelectric layer 903 , covering the etching shield layer 909 and the second end of the electrode layer 905 , and contacting the piezoelectric layer 903 .

[0317] In this embodiment, the material of the substrate 901 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0318] In this embodiment, the material of the piezoelectric layer 903 includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

[0319] In this embodiment, the piezoelectric layer 903 includes a plurality of crystals, and the plurality of crystals include a first crystal and a second crystal, wherein the first crystal and the second crystal are any two crystals of the plurality of crystals. A person skilled in the art knows that the crystal orientation, crystal plane, etc. of a crystal can be represented based on a coordinate system. Fig.17 As shown in FIG. 1 , for a hexagonal crystal, such as aluminum nitride crystal, an ac stereo coordinate system (including an a-axis and a c-axis) is used to represent it. Fig.18 As shown, for crystals of (i) orthorhombic system (a≠b≠c), (ii) tetragonal system (a=b≠c), (iii) cubic system (a=b=c), etc., an xyz three-dimensional coordinate system (including x-axis, y-axis and z-axis) is used for representation. In addition to the above two examples, crystals can also be represented based on other coordinate systems known to those skilled in the art, so the present invention is not limited to the above two examples.

[0320] In this embodiment, the first crystal can be represented based on a first three-dimensional coordinate system, and the second crystal can be represented based on a second three-dimensional coordinate system, wherein the first three-dimensional coordinate system at least includes a first coordinate axis along a first direction and a third coordinate axis along a third direction, and the second three-dimensional coordinate system at least includes a second coordinate axis along a second direction and a fourth coordinate axis along a fourth direction, wherein the first coordinate axis corresponds to the height of the first crystal, and the second coordinate axis corresponds to the height of the second crystal.

[0321] In this embodiment, the first direction and the second direction are the same or opposite. It should be noted that the first direction and the second direction are the same means that the angle between the vector along the first direction and the vector along the second direction ranges from 0 degrees to 5 degrees; the first direction and the second direction are opposite means that the angle between the vector along the first direction and the vector along the second direction ranges from 175 degrees to 180 degrees.

[0322] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the first coordinate axis is the first c-axis, and the third coordinate axis is the first a-axis; the second three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, wherein the first c-axis and the second c-axis point in the same or opposite directions.

[0323] In another embodiment, the first three-dimensional coordinate system further includes a fifth coordinate axis along a fifth direction, and the second three-dimensional coordinate system further includes a sixth coordinate axis along a sixth direction. In another embodiment, the first direction is the same as or opposite to the second direction, and the third direction is the same as or opposite to the fourth direction. It should be noted that the third direction is the same as the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 0 degrees to 5 degrees; the third direction is opposite to the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 175 degrees to 180 degrees.

[0324] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the first coordinate axis is the first z-axis, the third coordinate axis is the first y-axis, and the fifth coordinate axis is the first x-axis; the second three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the second coordinate axis is the second z-axis, the fourth coordinate axis is the second y-axis, and the sixth coordinate axis is the second x-axis. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in the same direction. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in the same direction.

[0325] In this embodiment, the piezoelectric layer 903 includes a plurality of crystals, and the half-peak width of the rocking curve of the plurality of crystals is less than 2.5 degrees. It should be noted that the rocking curve describes the angular divergence of a particular crystal plane (the crystal plane determined by the diffraction angle) in the sample, and is represented by a plane coordinate system, wherein the horizontal axis is the angle between the crystal plane and the sample plane, and the vertical axis represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the lattice quality, and the smaller the half-peak width angle, the better the lattice quality. In addition, the full width at half maximum (FWHM) refers to the distance between the two points where the function value is equal to half of the peak value in a peak of the function.

[0326] In this embodiment, the material of the electrode layer 905 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0327] In this embodiment, the material of the sacrificial layer 907 includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, polysilicon. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (ie, BCB), photosensitive epoxy resin photoresist (eg, SU-8), polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0328] In this embodiment, the material of the etching shield layer 909 includes but is not limited to at least one of the following: aluminum nitride, silicon carbide, diamond, silicon nitride, silicon dioxide, aluminum oxide, titanium dioxide. In this embodiment, the thickness of the etching shield layer 909 includes but is not limited to: 2 microns to 6 microns.

[0329] In this embodiment, the material of the intermediate layer 911 includes but is not limited to at least one of the following: polymer, insulating dielectric. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes but is not limited to at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide. In this embodiment, the thickness of the intermediate layer 911 includes but is not limited to: 20 microns to 100 microns. It should be noted that the acoustic impedance of the intermediate layer 911 can be small.

[0330] It should be noted that the piezoelectric layer 903 is formed on the substrate 901 , and the surface of the substrate 901 is flat, so the piezoelectric layer 903 may not include crystals with obvious turning, which helps to improve the electromechanical coupling coefficient and Q value of the resonant device.

[0331] In this embodiment, see Fig.10 , the method for forming the resonant device further includes: forming a second layer, wherein the forming the second layer includes:

[0332] Providing a substrate 1001;

[0333] An intermediate layer 1003 is formed and located on the substrate 1001 .

[0334] In this embodiment, the material of the substrate 1001 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0335] In this embodiment, the material of the intermediate layer 1003 includes but is not limited to: low surface energy chemical substances. In this embodiment, the low surface energy chemical substances include but are not limited to at least one of the following: 1H, 1H, 2H, 2H-perfluoroheptadecanetrimethyloxysilane, polydimethylsiloxane, hydrocarbons, fluorocarbons, polyethylene, polypropylene, polytetrafluoroethylene.

[0336] In this embodiment, see Fig.11 The method for forming the resonance device further includes: bonding the intermediate layer 911 and the intermediate layer 1003 .

[0337] In this embodiment, bonding the intermediate layer 911 and the intermediate layer 1003 includes: applying pressure to the intermediate layer 911 and the intermediate layer 1003 to bond the intermediate layer 911 and the intermediate layer 1003 .

[0338] In this embodiment, see Fig.12 , the method for forming the resonant device further comprises:

[0339] removing the substrate 901;

[0340] forming an electrode layer 1201, located on a second side of the piezoelectric layer 903, contacting the piezoelectric layer 903, wherein the second side is opposite to the first side;

[0341] The sacrificial layer 907 is removed by etching to form a cavity 1203, wherein the first end of the electrode layer 905 is located in the cavity 1203;

[0342] The intermediate layer 911 and the intermediate layer 1003 are separated to remove the intermediate layer 1003 and the substrate 1001 , that is, to remove the second layer.

[0343] In this embodiment, the material of the electrode layer 1201 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0344] In this embodiment, the etching method includes but is not limited to at least one of the following: oxygen ion etching, hydrofluoric acid etching, and xenon difluoride etching.

[0345] In this embodiment, separating the intermediate layer 911 and the intermediate layer 1003 includes: heating the intermediate layer 1003 to make the intermediate layer 1003 lose its viscosity, thereby separating the intermediate layer 911 and the intermediate layer 1003.

[0346] It should be noted that the etching shielding layer 909 can protect the intermediate layer 911 when the sacrificial layer 907 is etched away to form the cavity 1203. In addition, the etching shielding layer 909 can protect the resonance device from being corroded by water and oxygen.

[0347] In addition, removing the substrate 1001 can eliminate the electrical loss caused by the substrate 1001 .

[0348] In addition, the intermediate layer 1003 made of low surface energy material helps to easily remove the substrate 1001 and can better protect the substrate 1001 so that the substrate 1001 can be reused, thereby reducing production costs.

[0349] In addition, the electrode layer 905 , the piezoelectric layer 903 , and the electrode layer 1201 form a resonance zone, wherein the resonance zone is suspended relative to the cavity 1203 and has no overlapping portion with the intermediate layer 911 .

[0350] Figures 13 to 16 It is a schematic structural diagram of cross-section A of a method for forming a bulk acoustic wave resonance device according to an embodiment of the present invention.

[0351] like Fig.13As shown, an embodiment of the present invention provides a method for forming a bulk acoustic wave resonator device, including: forming a first layer, wherein the forming of the first layer includes:

[0352] Providing a substrate 1301;

[0353] An opening 1301a is formed at one end of the substrate 1301;

[0354] Forming a photolithography mark 1302 located in the opening 1301a;

[0355] Forming a piezoelectric layer 1303, located on the substrate 1301 and the photolithography mark 1302;

[0356] forming an electrode layer 1305 located on the piezoelectric layer 1303, wherein the electrode layer 1305 is located on a first side of the piezoelectric layer 1303;

[0357] forming the sacrificial layer 1307, which is located on the piezoelectric layer 1303 and covers the first end of the electrode layer 1305;

[0358] An intermediate layer 1309 is formed, located on the piezoelectric layer 1303 , covering the sacrificial layer 1307 and the second end of the electrode layer 1305 , and contacting the piezoelectric layer 1303 .

[0359] In this embodiment, the material of the substrate 1301 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0360] In this embodiment, the material of the photolithographic mark 1302 includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the piezoelectric layer 1303 includes but is not limited to at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate. In this embodiment, the material of the photolithographic mark 1302 is the same as the material of the piezoelectric layer 1303. In another embodiment, the material of the photolithographic mark 1302 and the material of the piezoelectric layer 1303 may be different.

[0361] In this embodiment, the piezoelectric layer 1303 includes a plurality of crystals, and the plurality of crystals include a first crystal and a second crystal, wherein the first crystal and the second crystal are any two crystals of the plurality of crystals. A person skilled in the art knows that the crystal orientation, crystal plane, etc. of a crystal can be represented based on a coordinate system. Fig.17 As shown in FIG. 1 , for a hexagonal crystal, such as aluminum nitride crystal, an ac stereo coordinate system (including an a-axis and a c-axis) is used to represent it. Fig.18As shown, for crystals of (i) orthorhombic system (a≠b≠c), (ii) tetragonal system (a=b≠c), (iii) cubic system (a=b=c), etc., an xyz three-dimensional coordinate system (including x-axis, y-axis and z-axis) is used for representation. In addition to the above two examples, crystals can also be represented based on other coordinate systems known to those skilled in the art, so the present invention is not limited to the above two examples.

[0362] In this embodiment, the first crystal can be represented based on a first three-dimensional coordinate system, and the second crystal can be represented based on a second three-dimensional coordinate system, wherein the first three-dimensional coordinate system at least includes a first coordinate axis along a first direction and a third coordinate axis along a third direction, and the second three-dimensional coordinate system at least includes a second coordinate axis along a second direction and a fourth coordinate axis along a fourth direction, wherein the first coordinate axis corresponds to the height of the first crystal, and the second coordinate axis corresponds to the height of the second crystal.

[0363] In this embodiment, the first direction and the second direction are the same or opposite. It should be noted that the first direction and the second direction are the same means that the angle between the vector along the first direction and the vector along the second direction ranges from 0 degrees to 5 degrees; the first direction and the second direction are opposite means that the angle between the vector along the first direction and the vector along the second direction ranges from 175 degrees to 180 degrees.

[0364] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the first coordinate axis is the first c-axis, and the third coordinate axis is the first a-axis; the second three-dimensional coordinate system is an ac three-dimensional coordinate system, wherein the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, wherein the first c-axis and the second c-axis point in the same or opposite directions.

[0365] In another embodiment, the first three-dimensional coordinate system further includes a fifth coordinate axis along a fifth direction, and the second three-dimensional coordinate system further includes a sixth coordinate axis along a sixth direction. In another embodiment, the first direction is the same as or opposite to the second direction, and the third direction is the same as or opposite to the fourth direction. It should be noted that the third direction is the same as the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 0 degrees to 5 degrees; the third direction is opposite to the fourth direction, which means that the angle between the vector along the third direction and the vector along the fourth direction ranges from 175 degrees to 180 degrees.

[0366] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the first coordinate axis is the first z-axis, the third coordinate axis is the first y-axis, and the fifth coordinate axis is the first x-axis; the second three-dimensional coordinate system is an xyz three-dimensional coordinate system, wherein the second coordinate axis is the second z-axis, the fourth coordinate axis is the second y-axis, and the sixth coordinate axis is the second x-axis. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in the same direction. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in the same direction, and the first y-axis and the second y-axis point in opposite directions. In another embodiment, the first z-axis and the second z-axis point in opposite directions, and the first y-axis and the second y-axis point in the same direction.

[0367] In this embodiment, the piezoelectric layer 1303 includes a plurality of crystals, and the half-peak width of the rocking curve of the plurality of crystals is less than 2.5 degrees. It should be noted that the rocking curve describes the angular divergence of a certain crystal plane (the crystal plane determined by the diffraction angle) in the sample, and is represented by a plane coordinate system, wherein the horizontal axis is the angle between the crystal plane and the sample plane, and the vertical axis represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the lattice quality, and the smaller the half-peak width angle, the better the lattice quality. In addition, the full width at half maximum (FWHM) refers to the distance between the two points where the function value is equal to half of the peak value in a peak of the function.

[0368] In this embodiment, the material of the electrode layer 1305 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0369] In this embodiment, the material of the sacrificial layer 1307 includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, polysilicon. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (ie, BCB), photosensitive epoxy resin photoresist (eg, SU-8), polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0370] In this embodiment, the material of the intermediate layer 1309 includes but is not limited to at least one of the following: polymer, insulating dielectric. In this embodiment, the polymer includes but is not limited to at least one of the following: benzocyclobutene (i.e., BCB), photosensitive epoxy resin photoresist (e.g., SU-8), polyimide. In this embodiment, the insulating dielectric includes but is not limited to at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide. In this embodiment, the thickness of the intermediate layer 1309 includes but is not limited to: 20 microns to 100 microns. It should be noted that the acoustic impedance of the intermediate layer 1309 can be small.

[0371] It should be noted that the piezoelectric layer 1303 is formed on the substrate 1301, and the surface of the substrate 1301 is flat, so the piezoelectric layer 1303 may not include crystals with obvious turning, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0372] In this embodiment, see Fig.14 The method for forming the resonant device further includes: forming a second layer, wherein the forming of the second layer includes: providing a substrate 1401.

[0373] In this embodiment, the material of the substrate 1401 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0374] In this embodiment, see Fig.15 The method for forming the resonant device further includes: bonding the intermediate layer 1309 and the substrate 1401 .

[0375] In this embodiment, bonding the intermediate layer 1309 and the substrate 1401 includes: applying pressure to the intermediate layer 1309 and the substrate 1401 to bond the intermediate layer 1309 and the substrate 1401 .

[0376] In this embodiment, see Fig.16 , the method for forming the resonant device further comprises:

[0377] The substrate 1301 is removed, and the photolithography mark 1302 is retained and located at one end of the piezoelectric layer 1303, wherein the photolithography mark 1302 is located at a second side of the piezoelectric layer 1303 and contacts the piezoelectric layer 1303, wherein the second side is opposite to the first side of the piezoelectric layer 1303;

[0378] Based on the photolithography mark 1302 , an electrode layer 1601 is formed, located on the second side and contacting the piezoelectric layer 1303 ;

[0379] The sacrificial layer 1307 is removed by etching to form a cavity 1603, wherein the first end of the electrode layer 1305 is located in the cavity 1603;

[0380] The base 1401 is removed by grinding.

[0381] In this embodiment, the material of the electrode layer 1601 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0382] In this embodiment, the etching method includes but is not limited to at least one of the following: oxygen ion etching, hydrofluoric acid etching, and xenon difluoride etching.

[0383] It should be noted that the photolithography mark 1302 has a calibration function, and the electrode layer 1601 is aligned relative to the photolithography mark 1302 to improve the accuracy.

[0384] In addition, removing the substrate 1401 can eliminate the electrical loss caused by the substrate 1401 .

[0385] In addition, the electrode layer 1305 , the piezoelectric layer 1303 , and the electrode layer 1601 form a resonance zone, wherein the resonance zone is suspended relative to the cavity 1603 and has no overlapping portion with the intermediate layer 1309 .

[0386] In general, the main beneficial effects of this embodiment include:

[0387] In summary, in the present invention, the piezoelectric layer is formed on the first substrate, and the surface of the first substrate is flat, so that the piezoelectric layer does not include crystals with obvious turning, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device. In addition, removing the second substrate can eliminate the electrical loss caused by the second substrate.

[0388] It should be understood that the examples and embodiments herein are merely illustrative and that various modifications and corrections may be made by those skilled in the art without departing from the spirit and scope of the present invention as defined in this application and the appended claims.

Claims

1. A method for forming a bulk acoustic wave resonator, characterized in that: include: A first layer is formed, wherein the forming of the first layer comprises: providing a first substrate; forming a piezoelectric layer, which is located on the first substrate; forming a first electrode layer, which is located on the piezoelectric layer; forming a cavity pretreatment layer, which is located on the piezoelectric layer and is used to form a cavity, wherein the cavity pretreatment layer at least covers the first end of the first electrode layer, and the cavity pretreatment layer is in contact with the piezoelectric layer, wherein the first side of the first layer corresponds to the first substrate side, and the second side of the first layer corresponds to the cavity pretreatment layer side; a second layer is formed, wherein the forming of the second layer comprises: providing a second substrate; bonding the first layer and the second layer, wherein the second layer is located on the second side; removing the first substrate, wherein the first side corresponds to the piezoelectric layer side; forming a second electrode layer, which is located on the first side and contacts the piezoelectric layer; and removing the second layer.

2. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein: The forming of the cavity pre-processing layer includes: forming a sacrificial layer located on the piezoelectric layer, wherein the sacrificial layer covers the first end.

3. The method for forming a bulk acoustic wave resonator device according to claim 2, wherein: The material of the sacrificial layer includes at least one of the following: polymer, silicon dioxide, doped silicon dioxide, and polysilicon.

4. The method for forming a bulk acoustic wave resonator device according to claim 3, wherein: The polymer includes at least one of the following: benzocyclobutene, photosensitive epoxy resin photoresist, and polyimide.

5. The method for forming a bulk acoustic wave resonator device according to claim 2, wherein: The forming of the cavity pretreatment layer further includes: forming a first intermediate layer located above the piezoelectric layer, the first intermediate layer at least covering the sacrificial layer, and the second side corresponds to the first intermediate layer side.

6. The method for forming a bulk acoustic wave resonator device according to claim 5, wherein: The first intermediate layer also covers the second end of the first electrode layer.

7. The method for forming a bulk acoustic wave resonator device according to claim 5, wherein: The material of the first intermediate layer includes at least one of the following: a polymer and an insulating dielectric.

8. The method for forming a bulk acoustic wave resonator device according to claim 7, wherein: The polymer includes at least one of the following: benzocyclobutene, photosensitive epoxy resin photoresist, and polyimide.

9. The method for forming a bulk acoustic wave resonator device according to claim 7, wherein: The insulating dielectric includes at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, and titanium oxide.

10. The method for forming a bulk acoustic wave resonator device according to claim 5, wherein: The thickness of the first intermediate layer is in a range of 20 micrometers to 100 micrometers.

11. The method for forming a bulk acoustic wave resonator device according to claim 5, wherein: Joining the first layer and the second layer includes bonding the first intermediate layer and the second substrate.

12. The method for forming a bulk acoustic wave resonator device according to claim 11, wherein: The removing of the second layer includes: removing the second substrate by grinding.

13. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein: The forming of the second layer further includes: forming a second intermediate layer located on the second substrate.

14. The method for forming a bulk acoustic wave resonator device according to claim 13, wherein: The material of the second intermediate layer includes a chemical substance with low surface energy.

15. The method for forming a bulk acoustic wave resonator device according to claim 14, wherein: The chemical substance with low surface energy includes at least one of the following: 1H, 1H, 2H, 2H-perfluoroheptadecantrimethyloxysilane, polydimethylsiloxane, hydrocarbons, fluorocarbons, polyethylene, polypropylene, and polytetrafluoroethylene.

16. The method for forming a bulk acoustic wave resonator device according to claim 13, wherein: Joining the first layer and the second layer includes bonding the cavity pretreatment layer and the second intermediate layer.

17. The method for forming a bulk acoustic wave resonator device according to claim 16, wherein: Removing the second layer includes: separating the cavity pretreatment layer and the second intermediate layer, and removing the second intermediate layer and the second substrate.

18. The method for forming a bulk acoustic wave resonator device according to claim 5, wherein: The forming of the second layer further includes: forming a second intermediate layer located on the second substrate.

19. The method for forming a bulk acoustic wave resonator device according to claim 18, wherein: The material of the second intermediate layer includes a chemical substance with low surface energy.

20. The method for forming a bulk acoustic wave resonator device according to claim 19, wherein: The chemical substance with low surface energy includes at least one of the following: 1H, 1H, 2H, 2H-perfluoroheptadecantrimethyloxysilane, polydimethylsiloxane, hydrocarbons, fluorocarbons, polyethylene, polypropylene, and polytetrafluoroethylene.

21. The method for forming a bulk acoustic wave resonator device according to claim 18, wherein: Joining the first layer and the second layer includes bonding the first intermediate layer and the second intermediate layer.

22. The method for forming a bulk acoustic wave resonator device according to claim 21, wherein: Removing the second layer includes: separating the first intermediate layer and the second intermediate layer, and removing the second intermediate layer and the second substrate.

23. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein: The piezoelectric layer includes multiple crystals, and the multiple crystals include a first crystal and a second crystal, wherein the first crystal and the second crystal are any two crystals among the multiple crystals; a first coordinate axis along a first direction corresponds to a height of the first crystal, and a second coordinate axis along a second direction corresponds to a height of the second crystal, wherein the first direction and the second direction are the same or opposite.

24. The method for forming a bulk acoustic wave resonator device according to claim 23, wherein: The first crystal corresponds to a first coordinate system, which includes the first coordinate axis and a third coordinate axis along a third direction; the second crystal corresponds to a second coordinate system, which includes the second coordinate axis and a fourth coordinate axis along a fourth direction.

25. The method for forming a bulk acoustic wave resonator device according to claim 24, wherein: The first coordinate system further includes a fifth coordinate axis along a fifth direction, and the second coordinate system further includes a sixth coordinate axis along a sixth direction.

26. The method for forming a bulk acoustic wave resonator device according to claim 25, wherein: The third direction is the same as or opposite to the fourth direction.

27. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein: The material of the piezoelectric layer includes at least one of the following: aluminum nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

28. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein: The piezoelectric layer includes a plurality of crystals, and a half-peak width of a rocking curve of the plurality of crystals is less than 2.5 degrees.

29. The method for forming a bulk acoustic wave resonator device according to claim 5, wherein: Also includes: The sacrificial layer is removed to form the cavity, wherein the first end is located in the cavity.

30. The method for forming a bulk acoustic wave resonator device according to claim 5, wherein: The forming of the cavity pretreatment layer further comprises: before forming the first intermediate layer, forming an etching shielding layer, which is located on the piezoelectric layer and at least covers the sacrificial layer.

31. The method for forming a bulk acoustic wave resonator device according to claim 30, characterized in that: The material of the etching shielding layer includes at least one of the following: aluminum nitride, silicon carbide, diamond, silicon nitride, silicon dioxide, aluminum oxide, and titanium dioxide.

32. The method for forming a bulk acoustic wave resonator device according to claim 30, wherein: The thickness of the etching shielding layer ranges from 2 microns to 6 microns.

33. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein: The forming of the piezoelectric layer includes: forming a first sub-piezoelectric layer located on the first substrate; and forming a second sub-piezoelectric layer located on the first sub-piezoelectric layer.

34. The method for forming a bulk acoustic wave resonator device according to claim 33, characterized in that: The half-peak width of the rocking curve of the first sub-piezoelectric layer is higher than 1.7 degrees; the half-peak width of the rocking curve of the second sub-piezoelectric layer is lower than 1.7 degrees.

35. The method for forming a bulk acoustic wave resonator device according to claim 33, wherein: Also includes: After removing the first substrate, the first sub-piezoelectric layer is removed, and the first side corresponds to the second sub-piezoelectric layer side.

36. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein: The forming of the first layer further comprises: forming a photolithography mark before forming the piezoelectric layer.

37. The method for forming a bulk acoustic wave resonator device according to claim 36, wherein: The forming of the photolithography mark comprises: forming an opening at one end of the first substrate; and forming the photolithography mark in the opening.

38. The method for forming a bulk acoustic wave resonator device according to claim 36, wherein: Also includes: After removing the first substrate, the photolithography mark is retained and located on the first side, contacting the piezoelectric layer.

39. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein: Also includes: Before forming the second electrode layer, an edge structure is formed, which is located on the first side and contacts the piezoelectric layer.

40. The method for forming a bulk acoustic wave resonator device according to claim 39, wherein: The forming of the second electrode layer includes: forming the second electrode layer located inside the edge structure.

41. The method for forming a bulk acoustic wave resonator device according to claim 39, wherein: The forming of the edge structure includes: forming a metal edge structure located on the first side and contacting the piezoelectric layer.

42. The method for forming a bulk acoustic wave resonator device according to claim 41, wherein: The forming of the edge structure further comprises: etching the inner side of the metal edge structure to form a slope surface.

43. The method for forming a bulk acoustic wave resonator device according to claim 42, wherein: The etching angle for etching the inner side of the metal edge structure includes: 1 degree to 89 degrees.

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