Method for forming a bulk acoustic wave resonator device

Abstract

Method for forming a bulk acoustic wave resonator device, comprising: forming a first layer, including: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer at least covering a first end of the first electrode layer, the cavity pretreatment layer contacting the piezoelectric layer and forming an acoustic reflection structure with the piezoelectric layer for blocking leakage waves, wherein a first side of the first layer corresponds to the first substrate side and a second side of the first layer corresponds to the cavity pretreatment layer side; forming a second layer, including: 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, the first side corresponding to the piezoelectric layer side; and forming a second electrode layer on the first side, contacting the piezoelectric layer. The present invention improves the electromechanical coupling coefficient and Q value of the resonator device. In addition, the processing of the second substrate and the processing of the active layer can be carried out separately, having flexibility.

Description

Technical Field

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

[0002] The radio frequency (RF) front-end chip of a wireless communication device includes a power amplifier, an antenna switch, a radio frequency filter, a duplexer, a multiplexer, a low-noise amplifier, etc. Among them, the radio frequency filter includes a surface acoustic wave (SAW) filter, a bulk acoustic wave (BAW) filter, a micro-electro-mechanical system (MEMS) filter, an integrated passive device (IPD), etc. The quality factor value (Q value) of SAW resonators and BAW resonators is relatively high. The radio frequency filters with low insertion loss and high out-of-band rejection made of SAW resonators and BAW resonators, namely SAW filters and BAW filters, are the mainstream radio frequency filters used in wireless communication devices 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 3 dB bandwidth of the resonator. The operating frequency of SAW filters is generally 0.4 GHz to 2.7 GHz, and the operating frequency of BAW filters is generally 0.7 GHz to 7 GHz.

[0003] Compared with SAW resonators, BAW resonators have better performance. However, 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 technologies such as carrier aggregation for overlapping use of frequency bands, the mutual interference between wireless frequency bands has become increasingly serious. High-performance BAW technology can solve the problem of mutual interference between frequency bands. With the advent of the 5G era, higher communication frequency bands have been introduced into wireless mobile networks. Currently, only BAW technology can solve the filtering problem in high-frequency bands.

[0004] Figure 1aA BAW filter circuit is shown, which includes a ladder circuit composed of multiple BAW resonators. Among them, f1, f2, f3, and f4 respectively represent four different frequencies. Inside each BAW resonator, metal electrodes on both sides of the resonator piezoelectric layer generate alternating positive and negative voltages. The piezoelectric layer generates sound waves through the alternating positive and negative voltages, and the sound waves in the resonator propagate in a direction perpendicular to the piezoelectric layer. To form resonance, the sound waves need to undergo total reflection on 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 sound wave reflection is that there is a large difference in acoustic impedance between the contact area of the upper surface of the upper metal electrode and the lower surface of the lower metal electrode and the acoustic impedance of the metal electrode.

[0005] A Film Bulk Acoustic Wave Resonator (FBAR) is a type of BAW resonator that can confine sound wave energy within the device. Above the resonance region of this resonator is air or vacuum, and there is a cavity below. The acoustic impedance of air is significantly different from that of the metal electrode, and sound waves can undergo total reflection on the upper surface of the upper metal electrode and the lower surface of the lower metal electrode to form a standing wave.

[0006] Figure 1b A schematic cross-sectional structure diagram of an FBAR 100 is shown. The FBAR 100 includes: a substrate 101, and the upper surface side of the substrate 101 includes a cavity 103; an electrode layer 105, located on the substrate 101 and the cavity 103; a piezoelectric layer 107, located on the substrate 101 and covering the electrode layer 105, and the piezoelectric layer 107 includes a protrusion 107a; an electrode layer 109, located on the piezoelectric layer 107, and the electrode layer 109 includes a protrusion 109a, and the protrusion 109a is located on the protrusion 107a; wherein, the resonance region 111 (i.e., the overlapping region of the electrode layer 105 and the protrusion 109a) is located on the cavity 103 and has an overlapping contact portion with the substrate 101. The FBAR 100 is formed by stacking layers one by one, that is, the electrode layer 105 is formed on the substrate 101, the piezoelectric layer 107 is formed on the electrode layer 105 and the substrate 101, and then the electrode layer 109 is formed on the piezoelectric layer 107. Since the electrode layer 105 protrudes, directly forming the piezoelectric layer 107 on the electrode layer 105 and the substrate 101 will cause obvious orientation of some grains in the piezoelectric layer 107 (for example, the grains in the two side portions 115 of the protrusion 107a) and they are not parallel to another part of the grains (for example, the grains in the middle portion 117 of the protrusion 107a), thereby reducing the electromechanical coupling coefficient and Q value of the FBAR. In addition, the FBAR 100 is formed by stacking layers one by one, lacking flexibility. Summary of the Invention

[0007] The problem solved by the present invention is to provide a method for forming a bulk acoustic wave resonator device, which can make the piezoelectric layer not include significantly oriented grains, thereby contributing to improving the electromechanical coupling coefficient of the resonator device and the Q value of the resonator device. In addition, the processing of the substrate and the processing of the active layer (at least including the piezoelectric layer, the lower electrode layer, such as the electrode layer 105, and the upper electrode layer, such as the electrode layer 109) can be carried out separately, making the method for forming the resonator device flexible.

[0008] To solve the above problems, an embodiment of the present invention provides a method for forming a bulk acoustic wave resonator device, including: forming a first layer, and the forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer at least covering a first end of the first electrode layer, the cavity pretreatment layer contacting the piezoelectric layer and forming an acoustic reflection structure with the piezoelectric layer for blocking leakage waves, wherein a first side of the first layer corresponds to the first substrate side, and a second side of the first layer corresponds to the cavity pretreatment layer side (that is, the first side and the second side are opposite); forming a second layer, and the forming of the second layer includes: 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, and the first side corresponds to the piezoelectric layer side; and forming a second electrode layer on the first side, contacting the piezoelectric 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 that the piezoelectric layer can not include significantly oriented grains, thereby contributing to improving the electromechanical coupling coefficient of the resonator device and the Q value of the resonator device. In addition, the processing of the second substrate and the processing of the active layer (at least including the piezoelectric layer, the first electrode layer and the second electrode layer) are carried out separately, making the method for forming the resonator device flexible.

[0010] In some embodiments, the forming of the cavity pretreatment layer includes: forming a sacrificial layer 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), photo-sensitive 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, forming the cavity pretreatment layer further includes: forming a first intermediate layer above the piezoelectric layer, the first intermediate layer covering at least the sacrificial layer, and the second side corresponding to the first intermediate layer. In some embodiments, the material of the first intermediate layer includes, but is not limited to, at least one of the following: polymers, insulating dielectrics. In some embodiments, the polymers include, but are 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 dielectrics include, but are not limited to, at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide. In some embodiments, the first intermediate layer also covers the second end of the first electrode layer.

[0012] In some embodiments, the material of the first substrate includes, but is not limited to, at least one of the following: silicon, silicon carbide, glass.

[0013] In some embodiments, the piezoelectric layer includes a plurality of grains, the plurality of grains including a first grain and a second grain, where the first grain and the second grain are any two grains among the plurality of grains; a first coordinate axis along a first direction corresponds to the height of the first grain, and a second coordinate axis along a second direction corresponds to the height of the second grain, where the first direction and the second direction are the same or opposite. It should be noted that the first direction and the second direction being the same means that the included angle range between the vector along the first direction and the vector along the second direction includes 0 degrees to 5 degrees; the first direction and the second direction being opposite means that the included angle range between the vector along the first direction and the vector along the second direction includes 175 degrees to 180 degrees.

[0014] In some embodiments, the first grain corresponds to a first coordinate system, the first coordinate system including the first coordinate axis and a third coordinate axis along a third direction; the second grain corresponds to a second coordinate system, the second coordinate system including the second coordinate axis and a fourth coordinate axis along a fourth direction.

[0015] 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 and the second direction are the same or opposite, and the third direction and the fourth direction are the same or opposite. It should be noted that the third direction and the fourth direction being the same means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 0 degrees to 5 degrees; the third direction and the fourth direction being opposite means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 175 degrees to 180 degrees.

[0016] In some embodiments, the material of the piezoelectric layer includes, but is not limited to, at least one of the following: aluminum nitride, aluminum gallium nitride, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

[0017] In some embodiments, the piezoelectric layer includes a plurality of grains, and the full width at half maximum of the rocking curve of the crystal formed by the plurality of grains is less than 2.5 degrees. It should be noted that the rocking curve describes the angular divergence of a specific crystal plane (the crystal plane with a determined diffraction angle) in the sample, which is represented by a plane coordinate system. Among them, the abscissa is the angle between the crystal plane and the sample surface, and the ordinate represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the crystal quality, and the smaller the full width at half maximum angle, the better the crystal quality. In addition, the full width at half maximum (FWHM) refers to the distance between two points with function values equal to half of the peak value in a peak of the function.

[0018] In some embodiments, forming the second layer further includes: forming a second intermediate layer above the second substrate. In some embodiments, the material of the second intermediate layer includes, but is not limited to, at least one of the following: polymers, insulating dielectrics. In some embodiments, the polymers include, but are 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 dielectrics include, but are not limited to, at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

[0019] In some embodiments, forming the second layer further includes: forming a thin film between the second substrate and the second intermediate layer. In some embodiments, the thin film includes, but is not limited to: polycrystalline thin films. In some embodiments, the material of the polycrystalline thin film includes, but is not limited to, at least one of the following: polysilicon, polycrystalline silicon nitride, polycrystalline silicon carbide. It should be noted that disposing the thin film between the second intermediate layer and the second substrate helps prevent the formation of a free electron layer on the surface of the second substrate, thereby reducing the electrical loss caused by the second substrate.

[0020] In some embodiments, the material of the second substrate includes, but is not limited to, at least one of the following: silicon, silicon carbide, glass.

[0021] In some embodiments, bonding the first layer and the second layer includes: bonding the first intermediate layer and the second intermediate layer to form a third intermediate layer. In some embodiments, the thickness of the third intermediate layer includes, but is not limited to: 0.1 micrometer to 10 micrometers. It should be noted that the acoustic impedance of the third intermediate layer is smaller than that of the piezoelectric layer, thereby blocking the leakage of sound waves from the resonant region into the second substrate.

[0022] In some embodiments, the material of the first electrode layer includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, aluminum; the material of the second electrode layer includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, aluminum.

[0023] 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.

[0024] In some embodiments, the forming the cavity pretreatment layer further includes: before forming the first intermediate layer, forming an etching mask layer on the piezoelectric layer, covering at least the sacrificial layer. In some embodiments, the material of the etching mask 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 mask layer includes but is not limited to: 0.1 micrometer to 3 micrometers. It should be noted that when etching to form the cavity, the etching mask layer can play a role in protecting the intermediate layer. In addition, the etching isolation mask layer can play a role in protecting the resonant device from corrosion by water and oxygen.

[0025] In some embodiments, forming the piezoelectric layer includes: forming a first sub-piezoelectric layer on the first substrate; forming a second sub-piezoelectric layer on the first sub-piezoelectric layer. In some embodiments, the full width at half maximum (FWHM) of the rocking curve of the first sub-piezoelectric layer is higher than 1.7 degrees; the FWHM 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, with the first side corresponding to the side of the second sub-piezoelectric layer. It should be noted that a rocking curve FWHM lower than 1.7 degrees indicates better crystal quality, and higher than 1.7 degrees indicates poorer crystal quality. When removing the first substrate, it will affect the crystal quality of the piezoelectric layer. Therefore, by using the piezoelectric layer with the above two-layer structure, after removing the first substrate, removing the first sub-piezoelectric layer with poorer quality and leaving the second sub-piezoelectric layer with better quality, the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device can be further improved.

[0026] In some embodiments, forming the first layer further includes: before forming the piezoelectric layer, forming a photolithography mark. In some embodiments, forming the photolithography mark includes: forming an opening at one end of the first substrate; forming the photolithography mark in the opening. In some embodiments, the method for forming the resonant device further includes: after removing the first substrate, retaining the photolithography mark on the first side, in contact with the piezoelectric layer.

[0027] In some embodiments, the method for forming the resonant device further includes: before forming the second electrode layer, forming an edge structure on the first side and in contact with the piezoelectric layer. In some embodiments, forming the second electrode layer includes: forming the second electrode layer inside the edge structure. It should be noted that the edge structure is located outside the edge of the second electrode layer to form a border for 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 within the resonant region. In some embodiments, the edge structure is a ring structure.

[0028] In some embodiments, forming the edge structure includes, but is not limited to: forming a metal edge structure on the first side and in contact with the piezoelectric layer. In some embodiments, forming the edge structure further 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 for etching the inner side of the metal edge structure includes, but is not limited to: 1 degree to 89 degrees. It should be noted that forming a slope on the inner side of the edge structure and keeping the outer side straight can increase the impedance of the edge structure, thereby better limiting the leakage of transverse waves.

[0029] It should be noted that the photolithography mark has a calibration function. Aligning the formation of the edge structure or the second electrode layer with respect to the photolithography mark can improve the accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1a is a schematic diagram of a bulk acoustic wave filter circuit;

[0031] Figure 1b is a schematic cross-sectional structure diagram of an FBAR 100;

[0032] Figure 2 is a schematic flowchart of a method 200 for forming a bulk acoustic wave resonant device according to an embodiment of the present invention;

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

[0034] Figure 3b is a schematic flowchart of a method 300b for forming a cavity pretreatment layer in a method 200 for forming a bulk acoustic wave resonant device according to an embodiment of the present invention;

[0035] Figure 3c is a schematic flowchart of a method 300c for forming a cavity pretreatment layer in a method 200 for forming a bulk acoustic wave resonant device according to an embodiment of the present invention;

[0036] Figure 4It is a schematic flow chart of the formation method of the second layer 400 in the formation method 200 of a bulk acoustic wave resonator according to an embodiment of the present invention;

[0037] Figures 5 to 10 It is a schematic cross-sectional structure diagram of the formation method of a bulk acoustic wave resonator according to an embodiment of the present invention;

[0038] Figures 11 to 14 It is a schematic cross-sectional structure diagram of the formation method of a bulk acoustic wave resonator according to an embodiment of the present invention;

[0039] Figures 15 to 18 It is a schematic cross-sectional structure diagram of the formation method of a bulk acoustic wave resonator according to an embodiment of the present invention;

[0040] Figure 19 It is a schematic structure diagram of a hexagonal crystal system grain;

[0041] Figure 20 (i) It is a schematic structure diagram of an orthorhombic crystal system grain;

[0042] Figure 20 (ii) It is a schematic structure diagram of a tetragonal crystal system grain;

[0043] Figure 20 (iii) It is a schematic structure diagram of a cubic crystal system grain. Detailed implementation manners

[0044] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following will describe the detailed implementation manners of the present invention with reference to the accompanying drawings.

[0045] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may be implemented in other ways different from those described herein, so the present invention is not limited by the specific embodiments disclosed below.

[0046] As described in the background art section, refer to Figure 1b , the FBAR 100 is formed by layer-by-layer stacking, that is, the electrode layer 105 is formed on the substrate 101, the piezoelectric layer 107 is formed on the electrode layer 105 and the substrate 101, and then the electrode layer 109 is formed on the piezoelectric layer 107. Since the electrode layer 105 protrudes, directly forming the piezoelectric layer 107 on the electrode layer 105 and the substrate 101 will cause some grains in the piezoelectric layer 107 (for example, the grains in the two side portions 115 of the protrusion 107a) to have an obvious orientation change and be non-parallel to another part of the grains (for example, the grains in the middle portion 117 of the protrusion 107a), thereby reducing the electromechanical coupling coefficient and Q value of the FBAR. In addition, the FBAR 100 is formed by layer-by-layer stacking, lacking flexibility.

[0047] The inventors of the present invention have found that when a piezoelectric layer is formed on a first substrate, since the surface of the first substrate is flat, the piezoelectric layer can be made to not include significantly turned crystal grains, thereby contributing to improving the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0048] The inventors of the present invention have also found that the processing of the second substrate and the processing of the active layer (at least including the piezoelectric layer, the lower electrode layer, such as the electrode layer 105 in the FBAR 100, and the upper electrode layer, such as the electrode layer 109 in the FBAR 100) can be carried out separately, so that the forming method of the resonant device has flexibility.

[0049] Furthermore, due to the lattice mismatch between the material of the first substrate and the material of the piezoelectric layer, based on different crystal qualities, the piezoelectric layer is divided into two sub-piezoelectric layers. Among them, the first sub-piezoelectric layer is a transition layer between the first substrate and the second sub-piezoelectric layer, and the crystal quality is poor. The second sub-piezoelectric layer is formed on the first sub-piezoelectric layer, and the crystal quality is good. If the first sub-piezoelectric layer with poor crystal quality cannot be removed, it will affect the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device. It should be noted that referring to Figure 1b , the FBAR 100 is formed by stacking layers one by one, and the piezoelectric layer 107 is directly formed on the electrode layer 105. Therefore, the sub-piezoelectric layer in contact with the electrode layer 105 with poor crystal quality cannot be removed.

[0050] The inventors of the present invention have found that after removing the first substrate, the first sub-piezoelectric layer with poor crystal quality can be further removed, leaving the second sub-piezoelectric layer with good crystal quality, thereby further improving the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0051] The inventors of the present invention have also found that the photolithography marks on the piezoelectric layer have a calibration function. Forming an edge structure or aligning the upper electrode layer with respect to the photolithography marks can improve the accuracy.

[0052] Figure 2 is a schematic flow chart of a forming method 200 of a bulk acoustic wave resonant device according to an embodiment of the present invention.

[0053] As Figure 2 shown, the forming method 200 of a bulk acoustic wave resonant device provided by an embodiment of the present invention includes:

[0054] Step S201, form the first layer. The forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity. The cavity pretreatment layer covers at least a first end of the first electrode layer, contacts the piezoelectric layer, and forms an acoustic reflection structure with the piezoelectric layer for blocking leakage waves. Wherein, a first side of the first layer corresponds to the side of the first substrate, and a second side of the first layer corresponds to the side of the cavity pretreatment layer (i.e., the first side and the second side are opposite).

[0055] Step S203, form the second layer. The forming of the second layer includes: providing a second substrate;

[0056] Step S205, bond the first layer and the second layer, wherein the second layer is located on the second side;

[0057] Step S207, remove the first substrate, and the first side corresponds to the side of the piezoelectric layer;

[0058] Step S209, form a second electrode layer on the first side, contacting the piezoelectric layer; and

[0059] Step S211, etch the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity.

[0060] 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 can be made not to include significantly turned grains, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device. In addition, the processing of the second substrate and the processing of the active layer (at least including the piezoelectric layer, the first electrode layer, and the second electrode layer) are carried out separately, which can make the forming method of the resonant device flexible.

[0061] In this embodiment, the material of the first substrate includes but is not limited to at least one of the following: silicon, silicon carbide, glass.

[0062] In this embodiment, the material of the piezoelectric layer includes but is not limited to at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate - lead titanate.

[0063] In this embodiment, the piezoelectric layer includes a plurality of grains, and the plurality of grains include a first grain and a second grain, where the first grain and the second grain are any two grains in the plurality of grains. Those skilled in the art know that the crystal orientation, crystal plane, etc. of the grains can be represented based on a coordinate system. For example Figure 19As shown, for grains of the hexagonal crystal system, such as aluminum nitride grains, an ac three-dimensional coordinate system (including the a-axis and the c-axis) is used for representation. As Figure 20 shown, for grains of (i) the orthorhombic crystal system (a≠b≠c), (ii) the tetragonal crystal system (a = b≠c), (iii) the cubic crystal system (a = b = c), etc., an xyz three-dimensional coordinate system (including the x-axis, the y-axis, and the z-axis) is used for representation. In addition to the above two examples, the grains can also be represented based on other coordinate systems known to those skilled in the relevant technical field. Therefore, the present invention is not limited by the above two examples.

[0064] In this embodiment, the first grain can be represented based on a first three-dimensional coordinate system, and the second grain can be represented based on a second three-dimensional coordinate system. Among them, 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. Among them, the first coordinate axis corresponds to the height of the first grain, and the second coordinate axis corresponds to the height of the second grain.

[0065] 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 being the same means that the included angle range between the vector along the first direction and the vector along the second direction includes 0 degrees to 5 degrees; the first direction and the second direction being opposite means that the included angle range between the vector along the first direction and the vector along the second direction includes 175 degrees to 180 degrees.

[0066] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, where 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, the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis. Among them, the first c-axis and the second c-axis point in the same or opposite directions.

[0067] 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 and the second direction are the same or opposite, and the third direction and the fourth direction are the same or opposite. It should be noted that the third direction and the fourth direction being the same means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 0 degrees to 5 degrees; the third direction and the fourth direction being opposite means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 175 degrees to 180 degrees.

[0068] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, where 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, 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.

[0069] In this embodiment, the piezoelectric layer includes a plurality of grains, and the full width at half maximum of the rocking curve of the crystal formed by the plurality of grains is less than 2.5 degrees. It should be noted that the rocking curve describes the angular divergence of a specific crystal plane (a crystal plane with a determined diffraction angle) in the sample, and is represented by a plane coordinate system. Among them, the abscissa is the angle between the crystal plane and the sample surface, and the ordinate represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the quality of the crystal, and the smaller the full width at half maximum angle, the better the crystal quality. In addition, the full width at half maximum (FWHM) refers to the distance between two points with function values equal to half of the peak value in a peak of the function.

[0070] 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.

[0071] In this embodiment, the material of the first electrode layer includes, but is not limited to, at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum; the material of the second electrode layer includes, but is not limited to, at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0072] In this embodiment, step S205 includes: bonding the cavity pretreatment layer and the second substrate. It should be noted that the acoustic impedance of the cavity pretreatment layer is smaller than that of the piezoelectric layer, so as to block the leakage of sound waves from the resonant region into the second substrate.

[0073] 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.

[0074] In one embodiment of the present invention, the method 200 for forming the resonant device includes:

[0075] Step S201, forming a first layer, where forming the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer covering at least a first end of the first electrode layer, the cavity pretreatment layer contacting the piezoelectric layer and forming an acoustic reflection structure with the piezoelectric layer for blocking leakage waves, wherein a first side of the first layer corresponds to the first substrate side, and a second side of the first layer corresponds to the cavity pretreatment layer side (i.e., the first side and the second side are opposite);

[0076] Step S203, forming a second layer, where forming the second layer includes: providing a second substrate;

[0077] Step S205, bonding the first layer and the second layer, where the second layer is located on the second side;

[0078] Step S207, removing the first substrate, the first side corresponding to the piezoelectric layer side;

[0079] Step S209, forming a second electrode layer on the first side, contacting the piezoelectric layer; and

[0080] Step S211, etching the cavity pretreatment layer to form the cavity, where the first end is located in the cavity.

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

[0082] Step S2011, forming a sacrificial layer on the piezoelectric layer, covering the first end;

[0083] Step S2013, forming an etching shielding layer on the piezoelectric layer, covering the sacrificial layer and a second end of the first electrode layer;

[0084] Step S2015, forming a first intermediate layer on the etching shielding layer, so that the second side corresponds to the first intermediate layer side, where the etching shielding 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 (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.

[0086] In this embodiment, the material of the etching shielding 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 shielding layer includes, but is not limited to: 0.1 micrometer to 3 micrometers.

[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: 0.1 micrometer to 10 micrometers.

[0088] In this embodiment, step S205 includes: bonding the first intermediate layer and the second substrate. It should be noted that the acoustic impedance of the first intermediate layer is smaller than that of the piezoelectric layer, thereby blocking the leakage of sound waves from the resonant region into the second substrate.

[0089] In this embodiment, step S211 includes: etching away 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, xenon difluoride etching.

[0090] It should be noted that the etching shielding layer can play a role in protecting the first intermediate layer when etching to form the cavity. In addition, the etching isolation shielding layer can protect the resonant device from corrosion by water and oxygen.

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

[0092] Step S201, form the first layer. The forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity. The cavity pretreatment layer at least covers the first end of the first electrode layer, contacts the piezoelectric layer, and forms an acoustic reflection structure with the piezoelectric layer for blocking leakage waves. Wherein, the first side of the first layer corresponds to the side of the first substrate, and the second side of the first layer corresponds to the side of the cavity pretreatment layer (i.e., the first side and the second side are opposite).

[0093] Step S203, form the second layer. The forming of the second layer includes: providing a second substrate;

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

[0095] Step S207, remove the first substrate, and the first side corresponds to the side of the piezoelectric layer;

[0096] Step S209, form a second electrode layer on the first side, contacting the piezoelectric layer; and

[0097] Step S211, etch the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity.

[0098] In this embodiment, as Figure 3b shown, the forming of the cavity pretreatment layer in step S201 includes:

[0099] Step S2011’, form a sacrificial layer on the piezoelectric layer, covering the first end;

[0100] Step S2013’, form an etching shielding layer on the piezoelectric layer, covering the sacrificial layer and the second end of the first electrode layer;

[0101] Step S2015’, form a first intermediate layer on the piezoelectric layer, covering the etching shielding layer, and contacting the piezoelectric layer, so that the second side corresponds to the side of the first intermediate layer.

[0102] 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 (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.

[0103] In this embodiment, the material of the etching mask 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 mask layer includes, but is not limited to: 0.1 micrometer to 3 micrometers.

[0104] 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: 0.1 micrometer to 10 micrometers.

[0105] In this embodiment, step S205 includes: bonding the first intermediate layer and the second substrate. It should be noted that the acoustic impedance of the first intermediate layer is smaller than that of the piezoelectric layer, thereby blocking the leakage of sound waves from the resonant region into the second substrate.

[0106] In this embodiment, step S211 includes: etching away 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, xenon difluoride etching.

[0107] It should be noted that the etching mask layer can play a role in protecting the first intermediate layer when etching to form the cavity. In addition, the etching isolation mask layer can protect the resonant device from corrosion by water and oxygen.

[0108] In one embodiment of the present invention, the forming method 200 of the resonant device includes:

[0109] Step S201, forming a first layer, and the forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer at least covering the first end of the first electrode layer, the cavity pretreatment layer contacting the piezoelectric layer and forming an acoustic reflection structure with the piezoelectric layer for blocking leakage waves, 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 (i.e., the first side and the second side are opposite);

[0110] Step S203, forming a second layer, and the forming of the second layer includes: providing a second substrate;

[0111] Step S205, bond the first layer and the second layer, wherein the second layer is located on the second side;

[0112] Step S207, remove the first substrate, the first side corresponding to the piezoelectric layer side;

[0113] Step S209, form a second electrode layer on the first side, contacting the piezoelectric layer; and

[0114] Step S211, etch the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity.

[0115] In this embodiment, as Figure 3c shown, the forming of the cavity pretreatment layer in step S201 includes:

[0116] Step S2011”, form a sacrificial layer on the piezoelectric layer, covering the first end;

[0117] Step S2013”, form an etching mask layer on the piezoelectric layer, covering the sacrificial layer;

[0118] Step S2015”, form a first intermediate layer on the piezoelectric layer, covering the etching mask layer and the second end of the first electrode layer, contacting the piezoelectric layer, so that the second side corresponds to the first intermediate layer side.

[0119] 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 (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.

[0120] In this embodiment, the material of the etching mask 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 mask layer includes but is not limited to: 0.1 micron to 3 microns.

[0121] 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: 0.1 micron to 10 microns.

[0122] In this embodiment, step S205 includes: bonding the first intermediate layer and the second substrate. It should be noted that the acoustic impedance of the first intermediate layer is smaller than that of the piezoelectric layer, thereby blocking the leakage of sound waves from the resonance region into the second substrate.

[0123] In this embodiment, step S211 includes: etching away 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, xenon difluoride etching.

[0124] It should be noted that the etching shielding layer can protect the first intermediate layer when the cavity is formed by etching. In addition, the etching isolation shielding layer can protect the resonance device from corrosion by water and oxygen.

[0125] In one embodiment of the present invention, the method 200 for forming the resonance device includes:

[0126] Step S201, forming a first layer, and the forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer at least covering the first end of the first electrode layer, the cavity pretreatment layer contacting the piezoelectric layer and forming an acoustic reflection structure with the piezoelectric layer for blocking leakage waves, 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 (i.e., the first side and the second side are opposite);

[0127] Step S203, forming a second layer, and the forming of the second layer includes: providing a second substrate;

[0128] Step S205, bonding the first layer and the second layer, wherein the second layer is located on the second side;

[0129] Step S207, removing the first substrate, and the first side corresponds to the piezoelectric layer side;

[0130] Step S209, forming a second electrode layer on the first side, contacting the piezoelectric layer; and

[0131] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity.

[0132] In this embodiment, as Figure 4 shown, step S203 includes:

[0133] Step S2031, provide the second substrate;

[0134] Step S2033, form a thin film on the second substrate; and

[0135] Step S2035, form a second intermediate layer on the thin film.

[0136] In this embodiment, the thin film includes but is not limited to: polycrystalline thin film. In this embodiment, the material of the polycrystalline thin film includes but is not limited to at least one of the following: polysilicon, polycrystalline silicon nitride, polycrystalline silicon carbide. It should be noted that disposing the thin film (for example, trap rich layer) between the second intermediate layer and the second substrate helps prevent the formation of a free electron layer on the surface of the second substrate, thereby reducing the electrical loss caused by the second substrate.

[0137] In this embodiment, the material of the second 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.

[0138] In this embodiment, step S205 includes: bonding the cavity pretreatment layer and the second intermediate layer to form a third intermediate layer. In this embodiment, the thickness of the third intermediate layer includes but is not limited to: 0.1 micrometer to 10 micrometers. It should be noted that the acoustic impedance of the third intermediate layer is smaller than that of the piezoelectric layer, thereby blocking the leakage of sound waves from the resonant region into the second substrate.

[0139] In one embodiment of the present invention, the forming method 200 of the resonant device includes:

[0140] Step S201, form a first layer, and the forming of the first layer includes: provide a first substrate; form a piezoelectric layer on the first substrate; form a first electrode layer on the piezoelectric layer; form a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer at least covers the first end of the first electrode layer, the cavity pretreatment layer contacts the piezoelectric layer, and forms an acoustic reflection structure with the piezoelectric layer for blocking leakage waves, 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 (i.e., the first side and the second side are opposite);

[0141] Step S203, form a second layer, and the forming of the second layer includes: provide a second substrate;

[0142] Step S205, bond the first layer and the second layer, wherein the second layer is located on the second side;

[0143] Step S207, remove the first substrate, where the first side corresponds to the side of the piezoelectric layer;

[0144] Step S209, form a second electrode layer on the first side, contacting the piezoelectric layer; and

[0145] Step S211, etch the cavity pretreatment layer to form the cavity, where the first end is located in the cavity.

[0146] In this embodiment, the forming of the cavity pretreatment layer in step S201 includes:

[0147] Form a sacrificial layer on the piezoelectric layer, covering the first end;

[0148] Form a first intermediate layer on the piezoelectric layer, covering the sacrificial layer and the second end of the first electrode layer, and contacting the piezoelectric layer, so that the second side corresponds to the side of the first intermediate layer.

[0149] 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 (i.e., BCB), photo-sensitive epoxy resin photoresist (e.g., SU-8), polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0150] 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), photo-sensitive 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.

[0151] In this embodiment, step S203 further includes: forming a second intermediate layer on the second substrate.

[0152] In this embodiment, the material of the second 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), photo-sensitive 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.

[0153] In this embodiment, step S205 includes: bonding the first intermediate layer and the second intermediate layer to form a third intermediate layer. In this embodiment, the thickness of the third intermediate layer includes but is not limited to: 0.1 micrometer to 10 micrometers. It should be noted that the acoustic impedance of the third intermediate layer is smaller than that of the piezoelectric layer, thereby blocking the leakage of sound waves from the resonance region into the second substrate.

[0154] In this embodiment, step S211 includes: etching away 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, xenon difluoride etching.

[0155] In one embodiment of the present invention, the forming method 200 of the resonant device includes:

[0156] Step S201, forming a first layer, and the forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer at least covering the first end of the first electrode layer, the cavity pretreatment layer contacting the piezoelectric layer and forming an acoustic reflection structure with the piezoelectric layer for blocking leakage waves, 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 (i.e., the first side and the second side are opposite);

[0157] Step S203, forming a second layer, and the forming of the second layer includes: providing a second substrate;

[0158] Step S205, joining the first layer and the second layer, wherein the second layer is located on the second side;

[0159] Step S207, removing the first substrate, and the first side corresponds to the piezoelectric layer side;

[0160] Step S209, forming a second electrode layer on the first side, contacting the piezoelectric layer; and

[0161] Step S211, etching the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity.

[0162] In this embodiment, the forming of the piezoelectric layer in step S201 includes: forming a first sub-piezoelectric layer on the first substrate; and forming a second sub-piezoelectric layer on the first sub-piezoelectric layer.

[0163] In this embodiment, the full width at half maximum (FWHM) of the rocking curve of the first sub-piezoelectric layer is higher than 1.7 degrees, and the FWHM 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 with a determined diffraction angle) in a sample, which is represented by a plane coordinate system. Among them, the abscissa is the angle between the crystal plane and the sample surface, and the ordinate represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the crystal quality. The smaller the FWHM angle, the better the crystal quality (that is, when the FWHM of the rocking curve is lower than 1.7 degrees, the crystal quality is better, and when it is higher than 1.7 degrees, the crystal quality is worse). In addition, the full width at half maximum (FWHM) refers to the distance between two points with function values equal to half of the peak value in a peak of a function.

[0164] 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, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-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, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-titanate. In this embodiment, the material of the first sub-piezoelectric layer is the same as that of the second sub-piezoelectric layer. In another embodiment, the material of the first sub-piezoelectric layer may be different from that of the second sub-piezoelectric layer.

[0165] In this embodiment, the second sub-piezoelectric layer includes a plurality of grains, and the plurality of grains include a first grain and a second grain. Among them, the first grain and the second grain are any two grains in the plurality of grains. Those skilled in the art know that the crystal orientation, crystal plane, etc. of the grains can be represented based on a coordinate system. As Figure 19 shown, for grains of the hexagonal crystal system, such as aluminum nitride grains, an ac three-dimensional coordinate system (including the a-axis and the c-axis) is used for representation. As Figure 20 shown, for grains of (i) the orthorhombic crystal system (a≠b≠c), (ii) the tetragonal crystal system (a = b≠c), (iii) the cubic crystal system (a = b = c), etc., an xyz three-dimensional coordinate system (including the x-axis, the y-axis, and the z-axis) is used for representation. In addition to the above two examples, the grains can also be represented based on other coordinate systems known to those skilled in the art. Therefore, the present invention is not limited by the above two examples.

[0166] In this embodiment, the first crystal grain can be represented based on a first three-dimensional coordinate system, and the second crystal grain 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 grain, and the second coordinate axis corresponds to the height of the second crystal grain.

[0167] 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 being the same means that the included angle range between the vector along the first direction and the vector along the second direction includes 0 degrees to 5 degrees; the first direction and the second direction being opposite means that the included angle range between the vector along the first direction and the vector along the second direction includes 175 degrees to 180 degrees.

[0168] 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, 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.

[0169] 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 and the second direction are the same or opposite, and the third direction and the fourth direction are the same or opposite. It should be noted that the third direction and the fourth direction being the same means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 0 degrees to 5 degrees; the third direction and the fourth direction being opposite means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 175 degrees to 180 degrees.

[0170] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, where 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, 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.

[0171] 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.

[0172] In this embodiment, step S209 includes: forming the second electrode layer to contact the second sub-piezoelectric layer.

[0173] It should be noted that the material of the first substrate and the material of the piezoelectric layer have a lattice mismatch. Based on different crystal qualities, the piezoelectric layer is divided into two sub-piezoelectric layers. Among them, the first sub-piezoelectric layer is a transition layer between the first substrate and the second sub-piezoelectric layer, and the crystal quality is poor; the second sub-piezoelectric layer is formed on the first sub-piezoelectric layer, and the crystal quality is good. In this embodiment, after removing the first substrate, the first sub-piezoelectric layer with poor crystal quality is further removed, leaving the second sub-piezoelectric layer with good crystal quality, so as to further improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0174] In an embodiment of the present invention, the method 200 for forming the resonant device includes:

[0175] Step S201, forming a first layer, and the forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer at least covers the first end of the first electrode layer, the cavity pretreatment layer contacts the piezoelectric layer, and forms an acoustic reflection structure with the piezoelectric layer for blocking leakage waves, where 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 (that is, the first side and the second side are opposite);

[0176] Step S203, form a second layer, and the forming of the second layer includes: providing a second substrate;

[0177] Step S205, bond the first layer and the second layer, wherein the second layer is located on the second side;

[0178] Step S207, remove the first substrate, and the first side corresponds to the side of the piezoelectric layer;

[0179] Step S209, form a second electrode layer on the first side, contacting the piezoelectric layer; and

[0180] Step S211, etch the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity.

[0181] In this embodiment, step S201 further includes: forming a photolithography mark before forming the piezoelectric layer. In this embodiment, the forming of the photolithography mark includes: forming an opening at one end of the first substrate; and forming the photolithography mark in the opening.

[0182] In this embodiment, the material of the photolithography mark includes but is not limited to at least one of the following: aluminum nitride, aluminum nitride alloy, 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, aluminum nitride alloy, 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 is the same as that of the piezoelectric layer. In another embodiment, the material of the photolithography mark and the material of the piezoelectric layer may be different.

[0183] In this embodiment, step S207 further includes: retaining the photolithography mark at one end of the piezoelectric layer, wherein the photolithography mark is located on the first side and contacts the piezoelectric layer.

[0184] In this embodiment, step S209 includes: forming the second electrode layer based on the photolithography mark.

[0185] It should be noted that the photolithography mark has a calibration function. Aligning the formation of the second electrode layer with respect to the photolithography mark can improve the accuracy.

[0186] In one embodiment of the present invention, the forming method 200 of the resonant device includes:

[0187] Step S201, form the first layer. The forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity. The cavity pretreatment layer at least covers a first end of the first electrode layer. The cavity pretreatment layer contacts the piezoelectric layer and forms an acoustic reflection structure with the piezoelectric layer for blocking leakage waves. Wherein, a first side of the first layer corresponds to the side of the first substrate, and a second side of the first layer corresponds to the side of the cavity pretreatment layer (i.e., the first side and the second side are opposite).

[0188] Step S203, form the second layer. The forming of the second layer includes: providing a second substrate;

[0189] Step S205, bond the first layer and the second layer, wherein the second layer is located on the second side;

[0190] Step S207, remove the first substrate, and the first side corresponds to the side of the piezoelectric layer;

[0191] Step S209, form a second electrode layer on the first side, contacting the piezoelectric layer; and

[0192] Step S211, etch the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity.

[0193] In this embodiment, step S201 further includes: forming a lithography mark before forming the piezoelectric layer. In this embodiment, the forming of the lithography mark includes: forming an opening at one end of the first substrate; and forming the lithography mark in the opening.

[0194] In this embodiment, the material of the lithography mark includes but is not limited to at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-titanate.

[0195] In this embodiment, the forming of the piezoelectric layer in step S201 includes: forming a first sub-piezoelectric layer on the first substrate and the lithography mark; and forming a second sub-piezoelectric layer on the first sub-piezoelectric layer.

[0196] In this embodiment, the full width at half maximum (FWHM) of the rocking curve of the first sub-piezoelectric layer is higher than 1.7 degrees, and the FWHM 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 with a determined diffraction angle) in the sample, which is represented by a plane coordinate system. Among them, the abscissa is the angle between the crystal plane and the sample surface, and the ordinate represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the crystal quality. The smaller the FWHM angle, the better the crystal quality (that is, when the FWHM of the rocking curve is lower than 1.7 degrees, the crystal quality is better, and when it is higher than 1.7 degrees, the crystal quality is worse). In addition, the full width at half maximum (FWHM) refers to the distance between two points with function values equal to half of the peak value in a peak of the function.

[0197] 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, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-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, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-titanate.

[0198] In this embodiment, the materials of the first sub-piezoelectric layer and the second sub-piezoelectric layer are the same. In another embodiment, the materials of the first sub-piezoelectric layer and the second sub-piezoelectric layer may be different. In this embodiment, the material of the lithography mark is the same as that of the first sub-piezoelectric layer. In another embodiment, the material of the lithography mark may be different from that of the first sub-piezoelectric layer.

[0199] In this embodiment, the second sub-piezoelectric layer includes a plurality of grains, and the plurality of grains include a first grain and a second grain. Among them, the first grain and the second grain are any two grains in the plurality of grains. Those skilled in the art know that the crystal orientation, crystal plane, etc. of the grains can be represented based on a coordinate system. As Figure 19 shown, for grains of the hexagonal crystal system, such as aluminum nitride grains, an ac stereoscopic coordinate system (including the a-axis and the c-axis) is used for representation. As Figure 20 shown, for grains of (i) the orthorhombic crystal system (a≠b≠c), (ii) the tetragonal crystal system (a = b≠c), (iii) the cubic crystal system (a = b = c), etc., an xyz stereoscopic coordinate system (including the x-axis, the y-axis, and the z-axis) is used for representation. In addition to the above two examples, the grains can also be represented based on other coordinate systems known to those skilled in the art. Therefore, the present invention is not limited by the above two examples.

[0200] In this embodiment, the first grain can be represented based on a first three-dimensional coordinate system, and the second grain can be represented based on a second three-dimensional coordinate system. Among them, 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. Among them, the first coordinate axis corresponds to the height of the first grain, and the second coordinate axis corresponds to the height of the second grain.

[0201] 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 being the same means that the included angle range between the vector along the first direction and the vector along the second direction includes 0 degrees to 5 degrees; the first direction and the second direction being opposite means that the included angle range between the vector along the first direction and the vector along the second direction includes 175 degrees to 180 degrees.

[0202] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, where 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, the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, where the first c-axis and the second c-axis point in the same or opposite directions.

[0203] 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 and the second direction are the same or opposite, and the third direction and the fourth direction are the same or opposite. It should be noted that the third direction and the fourth direction being the same means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 0 degrees to 5 degrees; the third direction and the fourth direction being opposite means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 175 degrees to 180 degrees.

[0204] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, where 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, 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.

[0205] 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 at one end of the second sub-piezoelectric layer, where the photolithography mark is located on the first side and contacts the second sub-piezoelectric layer.

[0206] In this embodiment, step S209 includes: forming the second electrode layer based on the photolithography mark to contact the second sub-piezoelectric layer.

[0207] It should be noted that the materials of the first substrate and the piezoelectric layer have a lattice mismatch. Based on different crystal qualities, the piezoelectric layer is divided into two sub-piezoelectric layers. Among them, the first sub-piezoelectric layer is a transition layer between the first substrate and the second sub-piezoelectric layer, and the crystal quality is poor; the second sub-piezoelectric layer is formed on the first sub-piezoelectric layer, and the crystal quality is good. In this embodiment, after removing the first substrate, the first sub-piezoelectric layer with poor crystal quality is further removed, leaving the second sub-piezoelectric layer with good crystal quality, so as to further improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0208] In addition, the photolithography mark has a calibration function. Forming the second electrode layer by aligning it with the photolithography mark can improve the accuracy.

[0209] In an embodiment of the present invention, the method 200 for forming the resonant device includes:

[0210] Step S201, form the first layer. The forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity. The cavity pretreatment layer covers at least a first end of the first electrode layer, contacts the piezoelectric layer, and forms an acoustic reflection structure with the piezoelectric layer for blocking leakage waves. Wherein, a first side of the first layer corresponds to the side of the first substrate, and a second side of the first layer corresponds to the side of the cavity pretreatment layer (i.e., the first side and the second side are opposite).

[0211] Step S203, form the second layer. The forming of the second layer includes: providing a second substrate;

[0212] Step S205, bond the first layer and the second layer, wherein the second layer is located on the second side;

[0213] Step S207, remove the first substrate, and the first side corresponds to the side of the piezoelectric layer;

[0214] Step S209, form a second electrode layer on the first side, contacting the piezoelectric layer; and

[0215] Step S211, etch the cavity pretreatment layer to form the cavity, wherein the first end is located in the cavity.

[0216] In this embodiment, the forming method 200 of the resonant device further includes: before step S209, form an edge structure on the first side, contacting the piezoelectric layer. In this embodiment, the edge structure is an annular structure.

[0217] In this embodiment, the forming of the edge structure includes: forming a metal edge structure on the first side, contacting the piezoelectric layer. In another embodiment, the forming of the edge structure includes: forming a polymer edge structure on the first side, contacting the piezoelectric layer; forming a metal edge structure on the polymer edge structure.

[0218] In this embodiment, the forming of the edge structure further includes: etching the inner side of the metal edge structure (i.e., the inner side of the edge structure) to form a slope. In this embodiment, the etching angle for etching the inner side of the metal edge structure includes but is not limited to: 1 degree to 89 degrees.

[0219] In this embodiment, step S209 includes: forming the second electrode layer on the inner side of the edge structure.

[0220] It should be noted that the edge structure is located outside the edge of the second electrode layer, forming a border around 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 resonant region, where the resonant region at least includes the piezoelectric layer, the first electrode layer, the edge structure and the second electrode layer. In addition, a slope is formed on the inner side of the edge structure, and a straight surface is maintained on the outer side, which can increase the impedance of the edge structure, thereby better limiting the leakage of transverse waves.

[0221] In an embodiment of the present invention, the forming method 200 of the resonant device includes:

[0222] Step S201, forming a first layer, and the forming of the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer at least covering a first end of the first electrode layer, the cavity pretreatment layer contacting the piezoelectric layer and forming an acoustic reflection structure with the piezoelectric layer for blocking leakage waves, where a first side of the first layer corresponds to the side of the first substrate, and a second side of the first layer corresponds to the side of the cavity pretreatment layer (i.e., the first side and the second side are opposite);

[0223] Step S203, forming a second layer, and the forming of the second layer includes: providing a second substrate;

[0224] Step S205, bonding the first layer and the second layer, where the second layer is located on the second side;

[0225] Step S207, removing the first substrate, and the first side corresponds to the side of the piezoelectric layer;

[0226] Step S209, forming a second electrode layer on the first side, contacting the piezoelectric layer; and

[0227] Step S211, etching the cavity pretreatment layer to form the cavity, where the first end is located in the cavity.

[0228] In this embodiment, step S201 further includes: forming a photolithography mark before forming the piezoelectric layer. In this embodiment, the forming of the photolithography mark includes: forming an opening at one end of the first substrate; and forming the photolithography mark in the opening.

[0229] In this embodiment, the materials of the photolithography marks include, but are not limited to, at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-titanate. In this embodiment, the materials of the piezoelectric layer include, but are not limited to, at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-titanate. In this embodiment, the materials of the photolithography marks are the same as those of the piezoelectric layer. In another embodiment, the materials of the photolithography marks and the piezoelectric layer may be different.

[0230] In this embodiment, step S207 further includes: retaining the photolithography mark at one end of the piezoelectric layer, where the photolithography mark is located on the first side and contacts the piezoelectric layer.

[0231] In this embodiment, the forming method 200 of the resonant device further includes: before step S209, forming an edge structure on the first side that contacts the piezoelectric layer based on the photolithography mark. In this embodiment, the edge structure is an annular structure.

[0232] In this embodiment, forming the edge structure includes: forming a metal edge structure on the first side that contacts the piezoelectric layer based on the photolithography mark. In another embodiment, forming the edge structure includes: forming a polymer edge structure on the first side that contacts the piezoelectric layer based on the photolithography mark; and forming a metal edge structure on the polymer edge structure.

[0233] In this embodiment, forming the edge structure further includes: etching the inner side of the metal edge structure (i.e., the inner side of the edge structure) to form a slope. In this embodiment, the etching angle for etching the inner side of the metal edge structure includes, but is not limited to, 1 degree to 89 degrees.

[0234] In this embodiment, step S209 includes: forming the second electrode layer on the inner side of the edge structure based on the photolithography mark.

[0235] It should be noted that the photolithography mark has a calibration function. Aligning the formation of the edge structure and the second electrode layer with respect to the photolithography mark can improve the accuracy.

[0236] In addition, the edge structure is located outside the edge of the second electrode layer, forming a border around 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 resonant region, where the resonant region at least includes the piezoelectric layer, the first electrode layer, the edge structure, and the second electrode layer. In addition, a slope is formed on the inner side of the edge structure, and a straight surface is maintained on the outer side, which can increase the impedance of the edge structure, thereby better limiting the leakage of transverse waves.

[0237] Combined with the cross-sectional structure schematic diagram of the bulk acoustic wave resonant device, the embodiments of the present invention provide the following three specific formation methods of the bulk acoustic wave resonant device for 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 by the specific embodiments disclosed below.

[0238] Figures 5 to 10 It is a cross-sectional structure schematic diagram of structure A of a formation method of a bulk acoustic wave resonant device according to an embodiment of the present invention.

[0239] As Figure 5 shown, the formation method of the resonant device includes: forming a first layer, where the forming of the first layer includes:

[0240] Providing a substrate 501;

[0241] Forming an opening 501a at one end of the substrate 501;

[0242] Forming a photolithography mark 502 in the opening 501a;

[0243] Forming a sub-piezoelectric layer 503 on the substrate 501 and the photolithography mark 502;

[0244] Forming a sub-piezoelectric layer 505 on the sub-piezoelectric layer 503.

[0245] In this embodiment, the material of the substrate 501 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0246] In this embodiment, the material of the photolithography mark 502 includes but is not limited to at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-titanate. In this embodiment, the material of the sub-piezoelectric layer 503 includes but is not limited to at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-titanate. In this embodiment, the materials of the photolithography mark 502 and the sub-piezoelectric layer 503 are the same. In another embodiment, the materials of the photolithography mark 502 and the sub-piezoelectric layer 503 may be different.

[0247] In this embodiment, the material of the sub-piezoelectric layer 505 includes, but is not limited to, at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, and lead magnesium niobate-titanate. In this embodiment, the materials of the sub-piezoelectric layer 503 and the sub-piezoelectric layer 505 are the same. In another embodiment, the materials of the sub-piezoelectric layer 503 and the sub-piezoelectric layer 505 may be different.

[0248] In this embodiment, the full width at half maximum (FWHM) of the rocking curve of the sub-piezoelectric layer 503 is higher than 1.7 degrees, and the FWHM of the rocking curve of the sub-piezoelectric layer 505 is lower than 1.7 degrees. It should be noted that the rocking curve describes the angular divergence of a specific crystal plane (a crystal plane with a determined diffraction angle) in a sample, and is represented by a plane coordinate system. Among them, the abscissa is the angle between the crystal plane and the sample surface, and the ordinate represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the crystal quality. The smaller the FWHM angle, the better the crystal quality (that is, when the FWHM of the rocking curve is lower than 1.7 degrees, the crystal quality is better, and when it is higher than 1.7 degrees, the crystal quality is worse). In addition, the full width at half maximum (FWHM) refers to the distance between two points with function values equal to half of the peak value in a peak of a function.

[0249] It should be noted that the lattice of the material of the substrate 501 does not match that of the piezoelectric layer. Based on different crystal qualities, the piezoelectric layer is divided into two sub-piezoelectric layers. Among them, the sub-piezoelectric layer 503 is a transition layer between the substrate 501 and the sub-piezoelectric layer 505, and the crystal quality is poor; the sub-piezoelectric layer 505 is formed on the sub-piezoelectric layer 503, and the crystal quality is good.

[0250] In this embodiment, the sub-piezoelectric layer 505 includes a plurality of grains, and the plurality of grains include a first grain and a second grain. Among them, the first grain and the second grain are any two grains in the plurality of grains. Those skilled in the art know that the crystal orientation, crystal plane, etc. of the grains can be represented based on a coordinate system. As Figure 19 shown, for grains of the hexagonal crystal system, such as aluminum nitride grains, an ac three-dimensional coordinate system (including the a-axis and the c-axis) is used for representation. As Figure 20 shown, for grains of (i) the orthorhombic crystal system (a≠b≠c), (ii) the tetragonal crystal system (a = b≠c), (iii) the cubic crystal system (a = b = c), etc., an xyz three-dimensional coordinate system (including the x-axis, the y-axis, and the z-axis) is used for representation. In addition to the above two examples, the grains can also be represented based on other coordinate systems known to those skilled in the art. Therefore, the present invention is not limited by the above two examples.

[0251] In this embodiment, the first crystal grain can be represented based on a first three-dimensional coordinate system, and the second crystal grain can be represented based on a second three-dimensional coordinate system. Among them, 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. Among them, the first coordinate axis corresponds to the height of the first crystal grain, and the second coordinate axis corresponds to the height of the second crystal grain.

[0252] 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 being the same means that the included angle range between the vector along the first direction and the vector along the second direction includes 0 degrees to 5 degrees; the first direction and the second direction being opposite means that the included angle range between the vector along the first direction and the vector along the second direction includes 175 degrees to 180 degrees.

[0253] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, where 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, the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, where the first c-axis and the second c-axis point in the same or opposite directions.

[0254] 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 and the second direction are the same or opposite, and the third direction and the fourth direction are the same or opposite. It should be noted that the third direction and the fourth direction being the same means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 0 degrees to 5 degrees; the third direction and the fourth direction being opposite means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 175 degrees to 180 degrees.

[0255] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, where 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, 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.

[0256] In this embodiment, referring to Figure 6 , forming the first layer further includes:

[0257] Forming an electrode layer 601 on the sub-piezoelectric layer 505, where the electrode layer 601 is located on the first side of the piezoelectric layer 505;

[0258] Forming a sacrificial layer 603 on the sub-piezoelectric layer 505 to cover the first end of the electrode layer 601;

[0259] Forming an etching mask layer 605 on the sub-piezoelectric layer 505 to cover the sacrificial layer 603 and the second end of the electrode layer 601;

[0260] Forming an intermediate layer 607 on the etching mask layer 605, where the etching mask layer 605 is located between the intermediate layer 607 and the sub-piezoelectric layer 505.

[0261] In this embodiment, the material of the electrode layer 601 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, aluminum.

[0262] In this embodiment, the material of the sacrificial layer 603 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 (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.

[0263] In this embodiment, the material of the etching mask layer 605 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 mask layer 605 includes but is not limited to: 0.1 micrometer to 3 micrometers.

[0264] In this embodiment, the material of the intermediate layer 607 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.

[0265] In this embodiment, referring to Figure 7 , the method for forming the resonant device further includes: forming a second layer, wherein forming the second layer includes:

[0266] Providing a substrate 701;

[0267] Forming a thin film 703 on the substrate 701;

[0268] Forming an intermediate layer 705 on the thin film 703.

[0269] In this embodiment, the material of the substrate 701 includes but is not limited to at least one of the following: silicon, silicon carbide, glass.

[0270] In this embodiment, the thin film 703 includes but is not limited to: polycrystalline thin film. In this embodiment, the material of the polycrystalline thin film includes but is not limited to at least one of the following: polysilicon, polycrystalline silicon nitride, polycrystalline silicon carbide. It should be noted that disposing the thin film 703 between the intermediate layer 705 and the substrate 701 helps prevent the formation of a free electron layer on the surface of the substrate 701, thereby reducing the electrical loss caused by the substrate 701.

[0271] In this embodiment, the material of the intermediate layer 705 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: silicon dioxide, silicon nitride, titanium oxide.

[0272] In this embodiment, referring to Figure 8 , the method for forming the resonant device further includes:

[0273] Bonding the intermediate layer 607 and the intermediate layer 705 to form an intermediate layer 801.

[0274] In this embodiment, the thickness of the intermediate layer 801 includes but is not limited to: 0.1 micrometer to 10 micrometers. It should be noted that the acoustic impedance of the intermediate layer 801 is smaller than that of the piezoelectric layer 505, thereby blocking the leakage of sound waves from the resonant region into the substrate 701.

[0275] In this embodiment, wafer bonding is performed on the intermediate layer 607 and the intermediate layer 705 to form the intermediate layer 801. In this embodiment, the wafer bonding employs but is not limited to one of the following two bonding techniques: polymer bonding technique, insulating dielectric bonding technique. In this embodiment, the polymer bonding technique includes: applying a polymer on the wafer; after the polymer is completely flattened, drying the polymer; and then performing wafer bonding. In this embodiment, the insulating dielectric bonding technique includes: forming an insulating dielectric layer on the wafer; performing a planarization process on the insulating dielectric layer; and then performing wafer bonding.

[0276] In this embodiment, referring to Figure 9 , the method for forming the resonant device further includes:

[0277] Removing the substrate 501;

[0278] Removing the sub-piezoelectric layer 503, and retaining the photolithography mark 502 at one end of the sub-piezoelectric layer 505, where the photolithography mark 502 is located on the second side of the sub-piezoelectric layer 505, and the second side is opposite to the first side of the sub-piezoelectric layer 505;

[0279] Based on the photolithography mark 502, forming an edge structure 901 on the second side in contact with the sub-piezoelectric layer 505.

[0280] In this embodiment, the edge structure 901 is an annular structure.

[0281] In this embodiment, forming the edge structure 901 includes: based on the photolithography mark 502, forming a metal edge structure on the second side in contact with the sub-piezoelectric layer 505. In another embodiment, forming the edge structure 901 includes: based on the photolithography mark 502, forming a polymer edge structure on the second side in contact with the sub-piezoelectric layer 505; and forming a metal edge structure on the polymer edge structure.

[0282] In another embodiment, forming the edge structure 901 further includes: etching the inner side of the metal edge structure (i.e., the inner side of the edge structure 901) 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.

[0283] It should be noted that after removing the substrate 501, further removing the sub-piezoelectric layer 503 and leaving the sub-piezoelectric layer 505 with better crystal quality can further improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0284] In this embodiment, referring to Figure 10 , the method for forming the resonant device further includes:

[0285] Based on the photolithography mark 502, an electrode layer 1001 is formed on the second side, contacting the sub-piezoelectric layer 505, wherein the electrode layer 1001 is located inside the edge structure 901;

[0286] Etch away the sacrificial layer 603 to form a cavity 1003, wherein the first end of the electrode layer 601 is located inside the cavity 1003.

[0287] In this embodiment, the material of the electrode layer 1001 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, aluminum.

[0288] In this embodiment, the etching method includes but is not limited to at least one of the following: oxygen ion etching, hydrofluoric acid etching, xenon difluoride etching.

[0289] It should be noted that the photolithography mark 502 has a calibration function. Aligning the formation of the edge structure 901 and the electrode layer 1001 with respect to the photolithography mark 502 can improve the accuracy.

[0290] In addition, the edge structure 901 is located outside the edge of the electrode layer 1001, forming a border around the electrode layer 1001, which is used to limit the leakage of transverse waves, thereby improving the Q value of the resonant device.

[0291] In addition, the edge structure 901 is located in the resonant region 1005, wherein the resonant region 1005 at least includes the sub-piezoelectric layer 505, the electrode layer 601, the edge structure 901 and the electrode layer 1001. The resonant region 1005 is suspended relative to the cavity 1003 and has no overlapping part with the intermediate layer 801.

[0292] In addition, a slope is formed inside the edge structure 901 and a straight surface is maintained outside, which can increase the impedance of the edge structure 901, thereby better limiting the leakage of transverse waves.

[0293] In addition, the etching shielding layer 605 can protect the intermediate layer 801 when removing the sacrificial layer 603 to form the cavity 1003. In addition, the etching isolation shielding layer 605 can protect the resonant device from corrosion by water and oxygen.

[0294] Generally speaking, the main beneficial effects of this embodiment include:

[0295] (1) The sub-piezoelectric layer 503 and the sub-piezoelectric layer 505 are formed on the substrate 501, and the surface of the substrate 501 is flat. Therefore, the sub-piezoelectric layer 505 can be made not to include significantly turned grains, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device;

[0296] (2) The processing of the substrate 701 and the processing of the active layer (at least including the piezoelectric layer 505, the electrode layer 601, the edge structure 901, and the electrode layer 1001) can be carried out separately, making the formation method of the resonant device flexible;

[0297] (3) The acoustic impedance of the intermediate layer 801 is smaller than that of the piezoelectric layer 505, thereby blocking the leakage of sound waves from the resonant region into the substrate 701;

[0298] (4) Arranging the thin film 703 between the intermediate layer 801 and the substrate 701 helps to prevent the formation of a free electron layer on the surface of the substrate 701, thereby reducing the electrical loss caused by the substrate 701;

[0299] (5) After removing the substrate 501, further removing the sub-piezoelectric layer 503 with relatively poor crystal quality and leaving the sub-piezoelectric layer 505 with better crystal quality can further improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device;

[0300] (6) The photolithography mark 502 has a calibration function. Aligning the formation of the edge structure 901 and the electrode layer 1001 relative to the photolithography mark 502 can improve the accuracy.

[0301] Figures 11 to 14 It is a schematic cross-sectional structure diagram of the profile A of a method for forming a bulk acoustic wave resonant device according to an embodiment of the present invention.

[0302] As Figure 11 shown, a method for forming a bulk acoustic wave resonant device provided by an embodiment of the present invention includes: forming a first layer, wherein the forming of the first layer includes:

[0303] Providing a substrate 1101;

[0304] Forming a piezoelectric layer 1103 on the substrate 1101;

[0305] Forming an electrode layer 1105 on the piezoelectric layer 1103, wherein the electrode layer 1105 is located on the first side of the piezoelectric layer 1103;

[0306] Form the sacrificial layer 1107, which is located on the piezoelectric layer 1103 and covers the first end of the electrode layer 1105;

[0307] Form the etching shielding layer 1109, which is located on the piezoelectric layer 1103 and covers the sacrificial layer 1107;

[0308] Form the intermediate layer 1111, which is located on the piezoelectric layer 1103, covers the second end of the etching shielding layer 1109 and the electrode layer 1105, and contacts the piezoelectric layer 1103.

[0309] In this embodiment, the material of the substrate 1101 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0310] In this embodiment, the material of the piezoelectric layer 1103 includes but is not limited to at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-lead titanate.

[0311] In this embodiment, the piezoelectric layer 1103 includes a plurality of grains, and the plurality of grains include a first grain and a second grain. Among them, the first grain and the second grain are any two grains in the plurality of grains. Those skilled in the art know that the crystal orientation, crystal plane, etc. of the grains can be represented based on a coordinate system. As Figure 19 shown, for grains of the hexagonal crystal system, such as aluminum nitride grains, an ac three-dimensional coordinate system (including the a-axis and the c-axis) is used for representation. As Figure 20 shown, for grains of (i) the orthorhombic crystal system (a≠b≠c), (ii) the tetragonal crystal system (a = b≠c), (iii) the cubic crystal system (a = b = c), etc., an xyz three-dimensional coordinate system (including the x-axis, the y-axis, and the z-axis) is used for representation. In addition to the above two examples, the grains can also be represented based on other coordinate systems known to those skilled in the art. Therefore, the present invention is not limited by the above two examples.

[0312] In this embodiment, the first grain can be represented based on a first three-dimensional coordinate system, and the second grain can be represented based on a second three-dimensional coordinate system. Among them, the first three-dimensional coordinate system includes at least a first coordinate axis along a first direction and a third coordinate axis along a third direction, and the second three-dimensional coordinate system includes at least a second coordinate axis along a second direction and a fourth coordinate axis along a fourth direction. Among them, the first coordinate axis corresponds to the height of the first grain, and the second coordinate axis corresponds to the height of the second grain.

[0313] 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 being the same means that the included angle range between the vector along the first direction and the vector along the second direction includes 0 degrees to 5 degrees; the first direction and the second direction being opposite means that the included angle range between the vector along the first direction and the vector along the second direction includes 175 degrees to 180 degrees.

[0314] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, where 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, the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, where the directions of the first c-axis and the second c-axis are the same or opposite.

[0315] 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 and the second direction are the same or opposite, and the third direction and the fourth direction are the same or opposite. It should be noted that the third direction and the fourth direction being the same means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 0 degrees to 5 degrees; the third direction and the fourth direction being opposite means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 175 degrees to 180 degrees.

[0316] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, where 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, 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 directions of the first z-axis and the second z-axis are the same, and the directions of the first y-axis and the second y-axis are the same. In another embodiment, the directions of the first z-axis and the second z-axis are opposite, and the directions of the first y-axis and the second y-axis are opposite. In another embodiment, the directions of the first z-axis and the second z-axis are the same, and the directions of the first y-axis and the second y-axis are opposite. In another embodiment, the directions of the first z-axis and the second z-axis are opposite, and the directions of the first y-axis and the second y-axis are the same.

[0317] In this embodiment, the piezoelectric layer 1103 includes a plurality of grains, and the full width at half maximum (FWHM) of the rocking curve of the crystal formed by the plurality of grains is less than 2.5 degrees. It should be noted that the rocking curve describes the angular divergence of a specific crystal plane (the crystal plane with a determined diffraction angle) in the sample, and is represented by a plane coordinate system. Among them, the abscissa is the angle between the crystal plane and the sample surface, and the ordinate represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the crystal quality, and the smaller the FWHM angle, the better the crystal quality. In addition, the full width at half maximum (FWHM) refers to the distance between the two points where the function values before and after are equal to half of the peak value in a peak of the function.

[0318] In this embodiment, the material of the electrode layer 1105 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0319] In this embodiment, the material of the sacrificial layer 1107 includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, and polysilicon. 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), and polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0320] In this embodiment, the material of the etching mask layer 1109 includes but is not limited to at least one of the following: aluminum nitride, silicon carbide, diamond, silicon nitride, silicon dioxide, aluminum oxide, and titanium dioxide. In this embodiment, the thickness of the etching mask layer 1109 includes but is not limited to: 0.1 micrometer to 3 micrometers.

[0321] In this embodiment, the material of the intermediate layer 1111 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), and 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, and titanium oxide.

[0322] It should be noted that the piezoelectric layer 1103 is formed on the substrate 1101, and the surface of the substrate 1101 is flat. Therefore, the piezoelectric layer 1103 can be made not to include significantly turned grains, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0323] In this embodiment, refer to Figure 12 , the method for forming the resonant device further includes: forming a second layer, where the forming of the second layer includes:

[0324] Provide a substrate 1201;

[0325] Form an intermediate layer 1203 on the substrate 1201.

[0326] In this embodiment, the material of the substrate 1201 includes but is not limited to at least one of the following: silicon, silicon carbide, glass.

[0327] In this embodiment, the material of the intermediate layer 1203 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.

[0328] In this embodiment, referring to Figure 13 , the method for forming the resonant device further includes: bonding the intermediate layer 1111 and the intermediate layer 1203 to form an intermediate layer 1301.

[0329] In this embodiment, the thickness of the intermediate layer 1301 includes but is not limited to: 0.1 micrometer to 10 micrometers.

[0330] In this embodiment, bonding the intermediate layer 1111 and the intermediate layer 1203 includes: performing wafer bonding on the intermediate layer 1111 and the intermediate layer 1203 to form the intermediate layer 1301. In this embodiment, the wafer bonding uses but is not limited to one of the following two bonding techniques: polymer bonding technique, insulating dielectric bonding technique. In this embodiment, the polymer bonding technique includes: applying a polymer on the wafer; drying the polymer after it is completely flat; and then performing wafer bonding. In this embodiment, the insulating dielectric bonding technique includes: forming an insulating dielectric layer on the wafer; performing planarization on the insulating dielectric layer; and then performing wafer bonding.

[0331] It should be noted that the acoustic impedance of the intermediate layer 1301 is smaller than that of the piezoelectric layer 1103, thereby blocking the leakage of sound waves from the resonant region into the substrate 1201.

[0332] In this embodiment, referring to Figure 14 , the method for forming the resonant device further includes:

[0333] Removing the substrate 1101;

[0334] Forming an electrode layer 1401 on the second side of the piezoelectric layer 1103, contacting the piezoelectric layer 1103, wherein the second side is opposite to the first side;

[0335] Etch away the sacrificial layer 1107 to form a cavity 1403, and a first end of the electrode layer 1105 is located within the cavity 1403.

[0336] In this embodiment, the material of the electrode layer 1401 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0337] 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.

[0338] It should be noted that the processing of the substrate 1201 and the processing of the active layer (including at least the piezoelectric layer 1103, the electrode layer 1105, and the electrode layer 1401) can be carried out separately, making the formation method of the resonant device flexible.

[0339] In addition, the etching shielding layer 1109 can protect the intermediate layer 1301 when the sacrificial layer 1107 is removed to form the cavity 1403. In addition, the etching isolation shielding layer 1109 can protect the resonant device from corrosion by water and oxygen.

[0340] In addition, a resonant region is formed in the overlapping region of the electrode layer 1105, the piezoelectric layer 1103, and the electrode layer 1401. Among them, the resonant region is suspended relative to the cavity 1403 and has no overlapping portion with the intermediate layer 1301.

[0341] Figures 15 to 18 It is a schematic cross-sectional view of structure A of a method for forming a bulk acoustic wave resonant device according to an embodiment of the present invention.

[0342] As Figure 15 shown, an embodiment of the present invention provides a method for forming a bulk acoustic wave resonant device, including: forming a first layer, where the forming of the first layer includes:

[0343] Providing a substrate 1501;

[0344] Forming an opening 1501a at one end of the substrate 1501;

[0345] Forming a photolithography mark 1502 in the opening 1501a;

[0346] Forming a piezoelectric layer 1503 on the substrate 1501 and the photolithography mark 1502;

[0347] Forming an electrode layer 1505 on the piezoelectric layer 1503, where the electrode layer 1505 is located on a first side of the piezoelectric layer 1503;

[0348] Form the sacrificial layer 1507, which is located on the piezoelectric layer 1503 and covers the first end of the electrode layer 1505;

[0349] Form the intermediate layer 1509, which is located on the piezoelectric layer 1503, covers the sacrificial layer 1507 and the second end of the electrode layer 1505, and contacts the piezoelectric layer 1503.

[0350] In this embodiment, the material of the substrate 1501 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0351] In this embodiment, the material of the photolithography mark 1502 includes but is not limited to at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-titanate. In this embodiment, the material of the piezoelectric layer 1503 includes but is not limited to at least one of the following: aluminum nitride, aluminum nitride alloy, gallium nitride, zinc oxide, lithium tantalate, lithium niobate, lead zirconate titanate, lead magnesium niobate-titanate. In this embodiment, the material of the photolithography mark 1502 is the same as the material of the piezoelectric layer 1503. In another embodiment, the material of the photolithography mark 1502 and the material of the piezoelectric layer 1503 may be different.

[0352] In this embodiment, the piezoelectric layer 1503 includes a plurality of grains, and the plurality of grains includes a first grain and a second grain. Among them, the first grain and the second grain are any two grains in the plurality of grains. Those skilled in the art know that the crystal orientation, crystal plane, etc. of the grains can be represented based on a coordinate system. As Figure 19 shown, for grains of the hexagonal crystal system, such as aluminum nitride grains, an ac three-dimensional coordinate system (including the a-axis and the c-axis) is used for representation. As Figure 20 shown, for grains of (i) the orthorhombic crystal system (a≠b≠c), (ii) the tetragonal crystal system (a = b≠c), (iii) the cubic crystal system (a = b = c), etc., an xyz three-dimensional coordinate system (including the x-axis, the y-axis, and the z-axis) is used for representation. In addition to the above two examples, the grains can also be represented based on other coordinate systems known to those skilled in the art. Therefore, the present invention is not limited by the above two examples.

[0353] In this embodiment, the first grain can be represented based on a first three-dimensional coordinate system, and the second grain can be represented based on a second three-dimensional coordinate system. Among them, the first three-dimensional coordinate system includes at least a first coordinate axis along a first direction and a third coordinate axis along a third direction, and the second three-dimensional coordinate system includes at least a second coordinate axis along a second direction and a fourth coordinate axis along a fourth direction. Among them, the first coordinate axis corresponds to the height of the first grain, and the second coordinate axis corresponds to the height of the second grain.

[0354] 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 being the same means that the included angle range between the vector along the first direction and the vector along the second direction includes 0 degrees to 5 degrees; the first direction and the second direction being opposite means that the included angle range between the vector along the first direction and the vector along the second direction includes 175 degrees to 180 degrees.

[0355] In another embodiment, the first three-dimensional coordinate system is an ac three-dimensional coordinate system, where 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, the second coordinate axis is the second c-axis, and the fourth coordinate axis is the second a-axis, where the directions of the first c-axis and the second c-axis are the same or opposite.

[0356] 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 and the second direction are the same or opposite, and the third direction and the fourth direction are the same or opposite. It should be noted that the third direction and the fourth direction being the same means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 0 degrees to 5 degrees; the third direction and the fourth direction being opposite means that the included angle range between the vector along the third direction and the vector along the fourth direction includes 175 degrees to 180 degrees.

[0357] In another embodiment, the first three-dimensional coordinate system is an xyz three-dimensional coordinate system, where 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, 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 directions of the first z-axis and the second z-axis are the same, and the directions of the first y-axis and the second y-axis are the same. In another embodiment, the directions of the first z-axis and the second z-axis are opposite, and the directions of the first y-axis and the second y-axis are opposite. In another embodiment, the directions of the first z-axis and the second z-axis are the same, and the directions of the first y-axis and the second y-axis are opposite. In another embodiment, the directions of the first z-axis and the second z-axis are opposite, and the directions of the first y-axis and the second y-axis are the same.

[0358] In this embodiment, the piezoelectric layer 1503 includes a plurality of grains, and the full width at half maximum (FWHM) of the rocking curve of the crystal composed of the plurality of grains is less than 2.5 degrees. It should be noted that the rocking curve describes the angular divergence of a specific crystal plane (the crystal plane with a determined diffraction angle) in the sample, and is represented by a plane coordinate system. Among them, the abscissa is the angle between the crystal plane and the sample surface, and the ordinate represents the diffraction intensity of the crystal plane at a certain angle. The rocking curve is used to represent the crystal quality, and the smaller the half-width angle, the better the crystal quality. In addition, the full width at half maximum (FWHM) refers to the distance between two points with function values equal to half of the peak value in a peak of the function.

[0359] In this embodiment, the material of the electrode layer 1505 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0360] In this embodiment, the material of the sacrificial layer 1507 includes but is not limited to at least one of the following: polymer, silicon dioxide, doped silicon dioxide, and polysilicon. 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), and polyimide. It should be noted that the doped silicon dioxide is silicon dioxide doped with other elements.

[0361] In this embodiment, the material of the intermediate layer 1509 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), and 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, and titanium oxide.

[0362] It should be noted that the piezoelectric layer 1503 is formed on the substrate 1501, and the surface of the substrate 1501 is flat. Therefore, the piezoelectric layer 1503 can be made to not include significantly turned grains, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device.

[0363] In this embodiment, referring to Figure 16 , the method for forming the resonant device further includes: forming a second layer, where the forming of the second layer includes:

[0364] Providing a substrate 1601;

[0365] Forming an intermediate layer 1603 on the substrate 1601.

[0366] In this embodiment, the material of the substrate 1601 includes but is not limited to at least one of the following: silicon, silicon carbide, and glass.

[0367] In this embodiment, the material of the intermediate layer 1603 includes but is not limited to at least one of the following: polymers, insulating dielectrics. In this embodiment, the polymers include but are 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 dielectrics include but are not limited to at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

[0368] In this embodiment, referring to Figure 17 , the method for forming the resonant device further includes: bonding the intermediate layer 1509 and the intermediate layer 1603 to form an intermediate layer 1701.

[0369] In this embodiment, the thickness of the intermediate layer 1701 includes but is not limited to: 0.1 micrometer to 10 micrometers.

[0370] In this embodiment, bonding the intermediate layer 1509 and the intermediate layer 1603 includes: performing wafer bonding on the intermediate layer 1509 and the intermediate layer 1603 to form the intermediate layer 1701. In this embodiment, the wafer bonding adopts but is not limited to one of the following two bonding techniques: polymer bonding technique, insulating dielectric bonding technique. In this embodiment, the polymer bonding technique includes: applying a polymer on the wafer; after the polymer is completely flattened, drying the polymer; and then performing wafer bonding. In this embodiment, the insulating dielectric bonding technique includes: forming an insulating dielectric layer on the wafer; performing planarization on the insulating dielectric layer; and then performing wafer bonding.

[0371] It should be noted that the acoustic impedance of the intermediate layer 1701 is smaller than that of the piezoelectric layer 1503, thereby blocking the leakage of sound waves from the resonant region into the substrate 1601.

[0372] In this embodiment, referring to Figure 18 , the method for forming the resonant device further includes:

[0373] removing the substrate 1501 and retaining the photolithography mark 1502 at one end of the piezoelectric layer 1503, where the photolithography mark 1502 is located on the second side of the piezoelectric layer 1503 and contacts the piezoelectric layer 1503, and the second side is opposite to the first side of the piezoelectric layer 1503;

[0374] forming an electrode layer 1801 on the second side based on the photolithography mark 1502 and contacting the piezoelectric layer 1503;

[0375] Etch away the sacrificial layer 1507 to form a cavity 1803, and the first end of the electrode layer 1505 is located within the cavity 1803.

[0376] In this embodiment, the material of the electrode layer 1801 includes but is not limited to at least one of the following: molybdenum, ruthenium, tungsten, platinum, iridium, and aluminum.

[0377] 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.

[0378] It should be noted that the photolithography mark 1502 has a calibration function. Aligning the electrode layer 1801 relative to the photolithography mark 1502 can improve the accuracy.

[0379] In addition, the processing of the substrate 1601 and the processing of the active layer (at least including the piezoelectric layer 1503, the electrode layer 1505, and the electrode layer 1801) can be carried out separately, making the formation method of the resonant device flexible.

[0380] In addition, the overlapping region of the electrode layer 1505, the piezoelectric layer 1503, and the electrode layer 1801 forms a resonant region, where the resonant region is suspended relative to the cavity 1803 and has no overlapping part with the intermediate layer 1701.

[0381] Generally speaking, the main beneficial effects of this embodiment include:

[0382] In summary, in the present invention, the piezoelectric layer is formed on the first substrate, and the surface of the first substrate is flat. Therefore, the piezoelectric layer can be made to not include significantly turned grains, which helps to improve the electromechanical coupling coefficient of the resonant device and the Q value of the resonant device. In addition, the processing of the second substrate and the processing of the active layer (at least including the piezoelectric layer, the lower electrode layer, and the upper electrode layer) can be carried out separately, making the formation method of the resonant device flexible. In addition, the acoustic impedance of the formed intermediate layer is smaller than that of the piezoelectric layer, thereby blocking the leakage of sound waves from the resonant region into the second substrate.

[0383] It should be understood that the examples and embodiments here are only exemplary, and those skilled in the art can make various modifications and corrections without departing from the spirit and scope of the present invention defined by the present application and the appended claims.

Claims

1. A method for forming a bulk acoustic wave resonator device, characterized in that, comprising: forming a first layer, wherein forming the first layer includes: providing a first substrate; forming a piezoelectric layer on the first substrate; forming a first electrode layer on the piezoelectric layer; forming a cavity pretreatment layer on the piezoelectric layer for forming a cavity, the cavity pretreatment layer at least covering a first end of the first electrode layer, wherein a first side of the first layer corresponds to the first substrate side, and a second side of the first layer corresponds to the cavity pretreatment layer side; forming a second layer, wherein forming the second layer includes: providing a second substrate; connecting the first layer and the second layer, wherein the second layer is located on the second side; removing the first substrate, the first side corresponding to the piezoelectric layer side; and forming a second electrode layer on the first side, contacting the piezoelectric layer; wherein forming the piezoelectric layer includes: forming a first sub-piezoelectric layer on the first substrate; forming a second sub-piezoelectric layer on the first sub-piezoelectric layer; after removing the first substrate, removing the first sub-piezoelectric layer, the first side corresponding to the second sub-piezoelectric layer side.

2. The method for forming a bulk acoustic wave resonator device according to claim 1, characterized in that, forming the cavity pretreatment layer includes: forming a sacrificial layer on the piezoelectric layer, the sacrificial layer covering the first end.

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

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

5. The method for forming a bulk acoustic wave resonator device according to claim 2, characterized in that, forming the cavity pretreatment layer further includes: forming a first intermediate layer above the piezoelectric layer, the first intermediate layer at least covering the sacrificial layer, the second side corresponding to the first intermediate layer side.

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

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

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

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

10. The method for forming a bulk acoustic wave resonator device according to claim 1, characterized in that, The piezoelectric layer includes a plurality of crystals, the plurality of crystals including a first crystal and a second crystal, where the first crystal and the second crystal are any two crystals among the plurality of crystals; a first coordinate axis in a first direction corresponds to the height of the first crystal, and a second coordinate axis in a second direction corresponds to the height of the second crystal, where the first direction and the second direction are the same or opposite.

11. The method for forming a bulk acoustic wave resonator device according to claim 10, characterized in that the first crystal corresponds to a first coordinate system, the first coordinate system including the first coordinate axis and a third coordinate axis in a third direction; the second crystal corresponds to a second coordinate system, the second coordinate system including the second coordinate axis and a fourth coordinate axis in a fourth direction.

12. The method for forming a bulk acoustic wave resonator device according to claim 11, characterized in that the first coordinate system further includes a fifth coordinate axis in a fifth direction, and the second coordinate system further includes a sixth coordinate axis in a sixth direction.

13. The method for forming a bulk acoustic wave resonator device according to claim 12, characterized in that the third direction and the fourth direction are the same or opposite.

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

15. The method for forming a bulk acoustic wave resonator device according to claim 1, characterized in that the piezoelectric layer includes a plurality of crystals, and the full width at half maximum of the rocking curve of the plurality of crystals is less than 2.5 degrees.

16. The method for forming a bulk acoustic wave resonator device according to claim 5, characterized in that forming the second layer further includes: forming a second intermediate layer above the second substrate.

17. The method for forming a bulk acoustic wave resonator device according to claim 16, characterized in that the material of the second intermediate layer includes at least one of the following: polymer, insulating dielectric.

18. The method for forming a bulk acoustic wave resonator device according to claim 17, characterized in that the polymer includes at least one of the following: benzocyclobutene, photosensitive epoxy resin photoresist, polyimide.

19. The method for forming a bulk acoustic wave resonator device according to claim 17, characterized in that the insulating dielectric includes at least one of the following: aluminum nitride, silicon dioxide, silicon nitride, titanium oxide.

20. The method for forming a bulk acoustic wave resonator device according to claim 16, characterized in that forming the second layer further includes: forming a thin film between the second substrate and the second intermediate layer.

21. The method for forming a bulk acoustic wave resonator device according to claim 20, characterized in that the thin film includes: polycrystalline thin film.

22. The method for forming a bulk acoustic wave resonator device according to claim 21, characterized in that the material of the polycrystalline thin film includes at least one of the following: polysilicon, polycrystalline silicon nitride, polycrystalline silicon carbide.

23. The method for forming a bulk acoustic wave resonator device according to claim 16, characterized in that Connecting the first layer and the second layer includes: bonding the first intermediate layer and the second intermediate layer to form a third intermediate layer.

24. The method for forming a bulk acoustic wave resonator device according to claim 23, wherein, the thickness of the third intermediate layer includes: 0.1 micrometer to 10 micrometers.

25. The method for forming a bulk acoustic wave resonator device according to claim 5, wherein, further comprising: removing the sacrificial layer to form the cavity, wherein the first end is located in the cavity.

26. The method for forming a bulk acoustic wave resonator device according to claim 5, wherein, the forming cavity pretreatment layer further includes: before forming the first intermediate layer, forming an etching mask layer on the piezoelectric layer, covering at least the sacrificial layer.

27. The method for forming a bulk acoustic wave resonator device according to claim 26, wherein, the material of the etching mask layer includes at least one of the following: aluminum nitride, silicon carbide, diamond, silicon nitride, silicon dioxide, aluminum oxide, titanium dioxide.

28. The method for forming a bulk acoustic wave resonator device according to claim 26, wherein, the thickness of the etching mask layer includes: 0.1 micrometer to 3 micrometers.

29. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein, the full width at half maximum of the rocking curve of the first sub-piezoelectric layer is higher than 1.7 degrees, and the full width at half maximum of the rocking curve of the second sub-piezoelectric layer is lower than 1.7 degrees.

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

31. The method for forming a bulk acoustic wave resonator device according to claim 30, wherein, forming the photolithography mark includes: forming an opening at one end of the first substrate; forming the photolithography mark in the opening.

32. The method for forming a bulk acoustic wave resonator device according to claim 30, wherein, further comprising: after removing the first substrate, retaining the photolithography mark on the first side, in contact with the piezoelectric layer.

33. The method for forming a bulk acoustic wave resonator device according to claim 1, wherein, further comprising: before forming the second electrode layer, forming an edge structure on the first side, in contact with the piezoelectric layer.

34. The method for forming a bulk acoustic wave resonator device according to claim 33, wherein, forming the second electrode layer includes: forming the second electrode layer inside the edge structure.

35. The method for forming a bulk acoustic wave resonator device according to claim 33, wherein, forming the edge structure includes: forming a metal edge structure on the first side, in contact with the piezoelectric layer.

36. The method for forming a bulk acoustic wave resonator device according to claim 35, wherein, forming the edge structure further includes: etching the inside of the metal edge structure to form a slope.

37. The method for forming a bulk acoustic wave resonator device according to claim 36, wherein, the etching angle for etching the inside of the metal edge structure includes: 1 degree to 89 degrees.

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