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

Abstract

A bulk acoustic wave resonator, a manufacturing method therefor, a filter and an electronic device. The bulk acoustic wave resonator comprises: a substrate; a first electrode, a piezoelectric thin film layer, and a second electrode which are stacked on the substrate, the piezoelectric thin film layer being arranged between the first electrode and the second electrode and covering the first electrode; a first reflective structure, the first reflective structure being arranged between the substrate and the piezoelectric thin film layer; and a second reflective structure, the second reflective structure being arranged on the substrate and embedded in the piezoelectric thin film layer. The bulk acoustic wave resonator, the manufacturing method therefor, the filter and the electronic device can increase Q values of small-area resonators, thereby improving the performance of the small-area resonators.

Description

Bulk acoustic wave resonator, preparation method thereof, filter, and electronic device

[0001] The present application claims priority to the Chinese patent application No. 202410994294.8, filed on July 23, 2024, and entitled "Bulk acoustic wave resonator, preparation method thereof, filter, and electronic device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] Embodiments of the present application relate to the technical field of filter, and particularly relate to a bulk acoustic wave resonator, a preparation method thereof, a filter, and an electronic device. BACKGROUND

[0003] With the development of communication technology, the requirements for core communication devices used to support information transmission in communication technology are becoming higher and higher. As a core device for realizing signal transmission, a radio frequency module usually needs to have performance parameters such as high frequency, large bandwidth, and low loss. In the radio frequency module, devices that play an important role include filters. In the prior art, bulk acoustic wave (BAW) filters based on acoustic resonance play an extremely important role in communication technology. Generally, a BAW filter is composed of multiple BAW resonators, and an important performance of a BAW resonator is the quality factor (Q). The higher the Q value, the higher the performance of the resonator, and the lower the insertion loss of the corresponding filter.

[0004] However, with the continuous development of communication technology, the communication frequency band is continuously increasing, and the increase of the communication frequency band leads to the continuous compression of the area of a single filter of a radio frequency front-end module, so the area of a single resonator is also becoming smaller and smaller. The reduction of the area of the resonator usually leads to the increase of the acoustic loss of the resonator, thereby reducing the Q value of the resonator. Therefore, how to improve the Q value of a small-area resonator to improve the performance of the resonator becomes a problem to be solved. SUMMARY

[0005] The bulk acoustic wave resonator, the preparation method thereof, the filter, and the electronic device provided by the embodiments of the present application can improve the Q value of the bulk acoustic wave resonator. To achieve the above-mentioned purpose, the embodiments of the present application adopt the following technical solutions:

[0006] In a first aspect, the embodiments of the present application provide a bulk acoustic wave resonator, comprising: a substrate; a piezoelectric thin film structure stacked on the substrate, the piezoelectric thin film structure comprising a first electrode, a piezoelectric thin film layer and a second electrode, the piezoelectric thin film layer being disposed between the first electrode and the second electrode and covering the first electrode; a first reflective structure disposed between the substrate and the second electrode structure; and a second reflective structure disposed on the substrate and embedded in the piezoelectric thin film layer, wherein the second reflective structure is disposed in the piezoelectric thin film layer.

[0007] The bulk acoustic wave resonator provided by the embodiments of the present application embeds the second reflective layer structure on the piezoelectric thin film layer, reflects the transverse leaky wave by using the second reflective structure, compensates for the problem that the ratio of the area of the bulk acoustic wave resonator to the perimeter of the bulk acoustic wave resonator decreases, thereby reducing the energy leakage of the transverse leaky wave, improving the Q value of the small-area resonator, and thus improving the performance of the small-area resonator.

[0008] Based on the first aspect, in a possible implementation manner, the first reflective structure is a first Bragg reflective structure, and the first Bragg reflective structure is stacked on the upper surface of the substrate; and the first electrode is disposed on the upper surface of the first Bragg reflective structure.

[0009] Based on the first aspect, in a possible implementation manner, the first reflective structure is a first cavity structure, the first cavity structure is embedded in the substrate and disposed on the side of the substrate close to the piezoelectric thin film structure; and the first electrode is disposed on the upper surface of the substrate.

[0010] Based on the first aspect, in a possible implementation manner, the second reflective structure is a second Bragg reflective structure, the second Bragg reflective structure comprises at least one low acoustic impedance structure and at least one high acoustic impedance structure, and the at least one low acoustic impedance structure and the at least one high acoustic impedance structure are alternately arranged along a direction perpendicular to the stacking direction.

[0011] Based on the first aspect, in a possible implementation manner, the material of each of the at least one low acoustic impedance structure comprises at least one of the following: silicon dioxide, silicon nitride, titanium or aluminum.

[0012] Based on the first aspect, in a possible implementation manner, the material of each of the at least one high acoustic impedance structure comprises at least one of the following: aluminum nitride, scandium-doped aluminum nitride, hafnium dioxide, hafnium nitride, tungsten nitride, tungsten trioxide, tantalum pentoxide, platinum, tantalum, tungsten or iridium.

[0013] Based on the first aspect, in a possible implementation manner, the material of any one of the at least one high acoustic impedance structure satisfies the following condition: the compression wave acoustic impedance of the any one of the at least one high acoustic impedance structure is greater than 0.5 times the compression wave acoustic impedance of the piezoelectric thin film layer.

[0014] In a possible implementation manner of the first aspect, a material of any one of the at least one low acoustic resistance structure satisfies the following condition: an acoustic impedance of a compression wave of any one of the at least one low acoustic resistance structure is less than an acoustic impedance of a shear wave of the piezoelectric thin film layer.

[0015] In a possible implementation manner of the first aspect, the second reflection structure is a second cavity structure, and the second cavity structure is embedded in the piezoelectric thin film layer.

[0016] In the second aspect, an embodiment of the present application provides a filter, which comprises an input terminal, an output terminal, a series branch and a parallel branch; one end of the series branch is connected to the input terminal, and the other end is connected to the output terminal; one end of the parallel branch is connected to the series branch, and the other end is grounded; the series branch comprises a first bulk acoustic wave resonator, and the parallel branch comprises a second bulk acoustic wave resonator; the first bulk acoustic wave resonator is the bulk acoustic wave resonator as described in the first aspect; and the second bulk acoustic wave resonator is the bulk acoustic wave resonator as described in the first aspect.

[0017] In the third aspect, an embodiment of the present application provides an electronic device, which comprises a transceiver, a memory and a processor, and the transceiver comprises the filter as described in the second aspect.

[0018] In the fourth aspect, an embodiment of the present application provides a method for manufacturing a bulk acoustic wave resonator, which comprises the following steps: providing a substrate; forming a first reflection structure on the substrate; forming a piezoelectric thin film structure on the first reflection structure, the piezoelectric thin film structure comprising a first electrode, a piezoelectric thin film layer and a second electrode, the piezoelectric thin film layer being arranged between the first electrode and the second electrode and covering the first electrode; and forming a second reflection structure on the substrate, the second reflection structure being embedded in the piezoelectric thin film layer.

[0019] It should be understood that the second aspect to the fourth aspect of the present application are consistent with the technical solution of the first aspect of the present application, and the beneficial effects obtained by each aspect and the corresponding possible implementation manners are similar, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0020] FIG. 1 is a structural schematic diagram of a bulk acoustic wave resonator in the prior art according to an embodiment of the present application;

[0021] FIG. 2 is a schematic diagram of a conductance curve of a bulk acoustic wave resonator according to an embodiment of the present application;

[0022] FIG. 3 is a schematic diagram of a comparison between a Q value curve of a small-area resonator and a Q value curve of a large-area resonator in the prior art according to an embodiment of the present application;

[0023] FIG. 4 is a top view of a bulk acoustic wave resonator according to an embodiment of the present application;

[0024] Fig. 5 is a sectional view of the resonator shown in Fig. 4 along AA' according to an embodiment of the present application;

[0025] Fig. 6A is another top view of a bulk acoustic resonator according to an embodiment of the present application;

[0026] Fig. 6B is another top view of a bulk acoustic resonator according to an embodiment of the present application;

[0027] Fig. 6C is another top view of a bulk acoustic resonator according to an embodiment of the present application;

[0028] Fig. 7A is a comparison of a Q value curve of a bulk acoustic resonator according to an embodiment of the present application and a Q value curve of a bulk acoustic resonator in the prior art;

[0029] Fig. 7B is a comparison of a Q value curve of another bulk acoustic resonator according to an embodiment of the present application and a Q value curve of a bulk acoustic resonator in the prior art;

[0030] Fig. 8 is another structural schematic diagram of a bulk acoustic resonator according to an embodiment of the present application;

[0031] Fig. 9 is a flow chart of a method for manufacturing the bulk acoustic resonator shown in Fig. 5 according to an embodiment of the present application;

[0032] Figs. 10A-10E are structural schematic diagrams of the bulk acoustic resonator shown in Fig. 5 during the manufacturing process according to an embodiment of the present application;

[0033] Figs. 11A-11F are structural schematic diagrams of the reflective structure shown in Fig. 5 during the manufacturing process according to an embodiment of the present application;

[0034] Fig. 12 is a structural schematic diagram of a filter according to an embodiment of the present application;

[0035] Fig. 13 is a structural schematic diagram of an electronic device according to an embodiment of the present application. DETAILED DESCRIPTION

[0036] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0037] The term "and / or" in this document merely describes an association relationship of associated objects, and indicates that there can be three relationships, for example, A and / or B can represent the three cases of A alone, A and B together, and B alone.

[0038] The terms "first", "second", and the like in the description of embodiments of the present application and in the claims of the present application are intended to distinguish different objects, or different processing of the same object, and are not intended to describe a particular sequential order, unless otherwise specified.

[0039] In addition, the terms "comprise", "comprising", "have", "having", "include", "including", "contain", "containing", and any variations thereof in the description of embodiments of the present application are intended to cover a non-exclusive inclusion. For example, a process, method, system, product, or device that comprises a list of steps or units is not limited to the listed steps or units, but can optionally further include other steps or units not listed, or can optionally further include other steps or units inherent to such process, method, product, or device.

[0040] It should be noted that in the description of embodiments of the present application, the words "exemplary" or "for example" are used to mean serving as an example, instance, or illustration. Any embodiment or design described as "exemplary" or "for example" in the present application is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the words "exemplary" or "for example" is intended to present concepts in a concrete manner.

[0041] In the description of embodiments of the present application, "a plurality of" means two or more, unless otherwise specified.

[0042] In existing communication technology, a radio frequency front-end module is usually provided with a filter to filter radio frequency transceiving signals. The filter of the radio frequency front-end is usually composed of a plurality of resonators, and a BAW resonator based on acoustic resonance is widely used in the filter of the radio frequency front-end module. As shown in FIG. 1, which is a structural schematic diagram of a BAW resonator in the prior art, the BAW resonator includes two opposite electrodes 1 and 2, and a piezoelectric layer arranged between the electrodes 1 and 2. The admittance amplitude response curve of the BAW resonator is shown in FIG. 2. As shown in the admittance amplitude response curve in FIG. 2, the abscissa is frequency (unit: MHz), and the ordinate is admittance amplitude response (unit: dB). As can be seen from FIG. 2, the admittance amplitude response includes a maximum value (i.e., a peak value) and a minimum value (i.e., a valley value), wherein the frequency fr corresponding to the maximum value of the admittance amplitude is the resonant frequency of the resonator, and the frequency fa corresponding to the minimum value of the admittance amplitude is the anti-resonant frequency. As can be seen from FIG. 2, the resonant frequency fr is near 4875 MHz, and the anti-resonant frequency fa is near 5200 MHz.

[0043] In addition, an important performance parameter of the BAW resonator is a quality factor Q value. The higher the Q value, the higher the performance of the resonator. That is, at the resonant frequency fr and the anti-resonant frequency fa shown in FIG. 1, the higher the Q value, the better the performance of the BAW resonator. However, with the continuous development of communication technology, the communication frequency band is continuously increasing, and the increase in the communication frequency band causes the area of a single filter of a radio frequency front-end module to be continuously compressed, and thus the area of a single resonator is also becoming smaller and smaller. The area of the resonator can refer to the area of the overlap of the electrode 1 and the electrode 2 in FIG. 1, or can be understood as the area of the projection of the electrode 1 on the electrode 2 being located in the electrode 2. The reduction of the area of the resonator usually causes the ratio of the area of the resonator to the circumference of the resonator to decrease, and the circumference of the resonator can refer to the boundary circumference of the overlapping region of the electrode 1 and the electrode 2 in FIG. 1. The above ratio decreases, thereby causing the energy leakage of the transverse leaky wave to increase, that is, the acoustic loss of the resonator increases, and the Q value is a ratio of the peak energy stored in a period to the dissipated energy, and the increase in the acoustic loss reduces the Q value of the resonator. As shown in FIG. 3, which is a Q value change curve of a small-area resonator and a large-area resonator, the abscissa is the frequency (unit: MHz), the ordinate is the Q value, the solid line is the Q value change curve of the small-area resonator, and the dashed line is the Q value change curve of the large-area resonator. As can be seen from FIG. 3, near the anti-resonant frequency shown in FIG. 2, that is, near the frequency of 5200 MHz, the Q value of the small-area resonator is much lower than that of the large-area resonator. Therefore, for the scenario of the small-area resonator, how to improve the Q value of the resonator to improve the performance of the resonator becomes a problem to be solved.

[0044] The BAW resonator provided by the embodiment of the present application sets the reflective layer in the peripheral region of the electrode layer on the substrate, reflects the transverse leaky wave by using the reflective layer, and compensates for the problem of the decrease in the ratio of the area of the resonator to the circumference of the resonator to reduce the Q value, thereby reducing the energy leakage of the transverse leaky wave, improving the Q value of the small-area resonator, and thus improving the performance of the small-area resonator. The bulk acoustic wave resonator provided by the embodiment of the present application can be a solidly mounted type resonator (SMR), and the SMR uses a Bragg reflective layer as a reflective boundary, for example, the embodiments shown in FIGS. 4 to 5 show the SMR structure. In addition, the bulk acoustic wave resonator provided by the embodiment of the present application can also be a thin film bulk acoustic resonator (FBAR), and the FBAR uses a solid-air interface as a reflective boundary, for example, the embodiment shown in FIG. 8 shows the FBAR structure. The BAW resonator provided by the embodiment of the present application will be described in more detail below in combination with the embodiments shown in FIGS. 4 to 8.

[0045] It is first noted that, in order to describe the features and elements of the film bulk acoustic resonator of the present application, the relative positions and orientations of the various components of the acoustic resonator will be described with reference to the x, y, and z directions in a Cartesian coordinate system. However, as will be understood by those skilled in the art, the relative positions and orientations of the various components can not be perfectly aligned, parallel, or perpendicular to one of these axes. For example, when layers are formed in a bulk acoustic resonator device, the top and bottom surfaces of the layers can not be perfectly flat surfaces, and they can not be perfectly parallel to each other. Likewise, the sidewalls of a layer or other features such as vias can not be perfectly perpendicular to their top and bottom surfaces, nor can they be perfectly parallel. Also, the various portions can have slightly sloped walls or surfaces, but for ease of illustration will be described as straight or planar. Thus, it is to be understood that references to the x, y, and z directions are intended to provide a general understanding of the orientation and position of the various portions relative to each other, and should not be interpreted as limiting.

[0046] Referring to FIG. 4, FIG. 4 is a top view of a bulk acoustic resonator 100 according to an embodiment of the present application, and FIG. 5 is a cross-sectional view of the bulk acoustic resonator along AA' as shown in FIG. 4. The structure of the bulk acoustic resonator 100 according to an embodiment of the present application will be described below with reference to FIGS. 4 and 5.

[0047] In the direction Z as shown in FIG. 5, the bulk acoustic resonator 100 includes a substrate 10, and a Bragg reflector structure 11, an electrode 122, a piezoelectric thin film layer 121, and an electrode 123 which are sequentially stacked on the substrate 10. The Bragg reflector structure 11 is disposed on a top surface of the substrate 10. The electrode 122, the piezoelectric thin film layer 121, and the electrode 123 form a sandwich structure. The electrode 122 is disposed on an upper surface of the Bragg reflector structure 11 away from the substrate 10, the piezoelectric thin film layer 121 is disposed on the upper surface of the Bragg reflector structure 11 and an upper surface of the electrode 122 and covers the electrode 122, and the electrode 123 is disposed on an upper surface of the piezoelectric thin film layer 121 away from the Bragg reflector structure 11.

[0048] The bulk acoustic resonator 100 further comprises a reflecting structure 13. The reflecting structure 13 is disposed on the upper surface of the Bragg reflecting structure 11 and embedded in the piezoelectric thin film layer 121. That is to say, the reflecting structure 13 is covered by the normal projection of the piezoelectric thin film layer 121 on the Bragg reflecting structure 11. As shown in FIG. 5, the reflecting structure 13 is embedded in the piezoelectric thin film layer 121. In one possible implementation, holes or grooves are disposed on the piezoelectric thin film layer 121 and penetrate the upper and lower surfaces of the piezoelectric thin film layer 121, and the holes or grooves on the piezoelectric thin film layer 121 are disposed in the region of the piezoelectric thin film layer 121 where no electrode 122 and electrode 123 are disposed. The reflecting structure 13 is filled in the holes or grooves disposed on the piezoelectric thin film layer 121 to be embedded in the piezoelectric thin film layer 121. In addition, the lower surface of the reflecting structure 13 is in contact with the upper surface of the Bragg reflecting structure 11, and the upper surface of the reflecting structure 13 can be flush with the upper surface of the piezoelectric thin film layer 121 (i.e., the surface where the electrode 123 is disposed) and exposed. In another possible implementation, the reflecting structure 13 is embedded in the piezoelectric thin film layer 121 and buried in the piezoelectric thin film layer 121. The embodiments of the present application do not make specific limitation on the position of the reflecting structure 13 embedded in the piezoelectric thin film layer 121 along the direction Z.

[0049] As shown in FIG. 4, the reflecting structure 13 is disposed in the peripheral region of the electrode 123 in the plane formed along the x direction and y direction. The electrode 123 can include two edges S1 and S2 extending along the x direction and oppositely disposed along the y direction, and in addition, the electrode 123 can further include two edges S3 and S4 extending along the y direction and oppositely disposed along the x direction.

[0050] In one possible implementation, the reflecting structure 13 can be disposed on the side close to any one edge of the electrode 123, for example, the reflecting structure 13 can be disposed on the side close to the edge S1 of the electrode 123, the reflecting structure 13 can be disposed on the side close to the edge S2 of the electrode 123, the reflecting structure 13 can be disposed on the side close to the edge S3 of the electrode 123, and the reflecting structure 13 can be disposed on the side close to the edge S4 of the electrode 123. As shown in FIG. 6A, FIG. 6A schematically shows that the reflecting structure 13 is disposed on the side close to the edge S1 of the electrode 123.

[0051] In a possible implementation, the reflective structure 13 can be arranged on one side of any two edges of the electrode 123, for example, the two edges can be adjacent edges, and can be opposite edges. For example, the reflective structure 13 can be arranged on one side of the edge S1 and one side of the edge S2 of the electrode 123; for example, the reflective structure 13 can be arranged on one side of the edge S1 and one side of the edge S3 of the electrode 123; for example, the reflective structure 13 can be arranged on one side of the edge S1 and one side of the edge S4 of the electrode 123; for example, the reflective structure 13 can be arranged on one side of the edge S2 and one side of the edge S3 of the electrode 123; for example, the reflective structure 13 can be arranged on one side of the edge S2 and one side of the edge S4 of the electrode 123; for example, the reflective structure 13 can be arranged on one side of the edge S3 and one side of the edge S4 of the electrode 123. As shown in FIG. 6B, FIG. 6B schematically shows that the reflective structure 13 is arranged on one side of the edge S1 and one side of the edge S2 of the electrode 123.

[0052] In a possible implementation, the reflective structure 13 can be arranged on one side of any three edges of the electrode 123. For example, the reflective structure 13 can be arranged on one side of the edge S1, the edge S2, and the edge S3 of the electrode 123, and the side of the edge S4 of the electrode 123 is not provided with the reflective structure 13; for example, the reflective structure 13 can be arranged on one side of the edge S1, the edge S2, and the edge S4 of the electrode 123, and the side of the edge S3 of the electrode 123 is not provided with the reflective structure 13; for example, the reflective structure 13 can be arranged on one side of the edge S1, the edge S3, and the edge S4 of the electrode 123, and the side of the edge S2 of the electrode 123 is not provided with the reflective structure 13; for example, the reflective structure 13 can be arranged on one side of the edge S2, the edge S3, and the edge S4 of the electrode 123, and the side of the edge S1 of the electrode 123 is not provided with the reflective structure 13. As shown in FIG. 6C, FIG. 6C schematically shows that the reflective structure 13 is arranged on one side of the edge S1, the edge S2, and the edge S3 of the electrode 123.

[0053] In a possible implementation, the reflective structure 13 is arranged on all sides of the electrode 123, as shown in FIG. 4, which schematically shows a case in which the reflective structure 13 is arranged on all sides of the electrode 123. As shown in FIG. 4, the reflective structure 13 is arranged on one side of each of the edge S1, the edge S2, the edge S3, and the edge S4 of the electrode 123.

[0054] It should be noted that when at least three sides of the electrode 123 are provided with the reflection structure 13, the reflection structure 13 can be a continuous structure or a discontinuous structure; similarly, when two adjacent sides of the electrode 123 are provided with the reflection structure 13, the reflection structure 13 can be a continuous structure or a discontinuous structure. For example, FIG. 6C shows that the reflection structure 13 is a discontinuous structure, that is, the reflection structure 13 on the side S1 and the side S3 of the electrode 123 is continuous, and the reflection structure 13 on the side S2 of the electrode 123 is discontinuous from the reflection structure 13 on the other two sides. For another example, FIG. 4 shows that the reflection structure 13 is a continuous structure.

[0055] It should also be noted that, as shown in the top views of FIGS. 4, 6A-6C, the reflection structure 13 is schematically shown as a quadrilateral. In other possible implementations, the pattern of the reflection structure 13 can also be other shapes in the plane formed by the direction x and the direction y, for example, can be a polygon, and can also be an irregular figure, for example, an irregular quadrilateral, an irregular pentagon, etc., and the shape of the reflection structure 13 is not limited in the embodiments of the present application.

[0056] On the basis of any possible implementation described above, the reflection structure 13 shown in the embodiments of the present application can be a Bragg reflection structure. As shown in FIG. 4, when the reflection structure 13 is a Bragg reflection structure, the Bragg reflection structure 13 includes at least one low acoustic impedance structure 131 and at least one high acoustic impedance structure 132, and the at least one low acoustic impedance structure 131 and the at least one high acoustic impedance structure 132 are alternately arranged along the direction X or the direction Y (i.e., along a direction perpendicular to the direction Z) from the direction close to the electrode 123 to the direction away from the electrode 123. FIGS. 4-6C schematically show three low acoustic impedance structures 131 and two high acoustic impedance structures 132. It can be understood that the number of layers of the low acoustic impedance structure 131 and the number of layers of the high acoustic impedance structure 132 included in the Bragg reflection structure 13 are not limited in the embodiments of the present application, and can be set according to the needs of the application scenario. As can be seen from FIG. 4, one high acoustic impedance structure 132 is arranged between every two low acoustic impedance structures 131. In other possible implementations, three high acoustic impedance structures 132 and two low acoustic impedance structures 131 can be arranged, and one low acoustic impedance structure 131 is arranged between every two high acoustic impedance structures 132. It should be understood that the low acoustic impedance structure 131 and the high acoustic impedance structure 132 are both for the parameter of acoustic impedance, which can also be expressed as "the product of medium density and acoustic velocity". The low acoustic impedance structure 131 refers to a structure formed by a material with low acoustic impedance, and the high acoustic impedance structure 132 refers to a structure formed by a material with high acoustic impedance, and the high and low of the acoustic impedance of the two structures are relative.

[0057] In the embodiments of the present application, the material of any one of the low acoustic impedance structures 131 satisfies the following condition: the compressional wave acoustic impedance of the material of the low acoustic impedance structure 131 is less than the shear wave acoustic impedance of the material of the piezoelectric thin film layer 121. In a possible implementation, the material of the low acoustic impedance structure 131 can include but is not limited to: a dielectric material such as silicon dioxide (SiO2), silicon nitride (SiN), titanium (Ti), or aluminum (Al). In a possible implementation, the material of the piezoelectric thin film layer 121 can include but is not limited to: a material such as lead zirconate titanate piezoelectric ceramic (PZT), zinc oxide (ZnO), gallium nitride (GaN), aluminum nitride (AlN), scandium-doped aluminum nitride (AlScN), lithium carbonate (LiTaO3), or lithium niobate (LiNbO3).

[0058] In the embodiments of the present application, the material of any one of the high acoustic impedance structures 132 satisfies the following condition: the compressional wave acoustic impedance of the high acoustic impedance structure 132 is greater than 0.5 times the compressional wave acoustic impedance of the piezoelectric thin film layer 121. In a possible implementation, the material of the high acoustic impedance structure 132 can include but is not limited to: aluminum nitride (AlN), scandium-doped aluminum nitride (AlScN), hafnium dioxide (HfO2), hafnium nitride (HfN), tungsten nitride (WN), tungsten trioxide (WO3), tantalum pentoxide (Ta2O5), platinum (Pt), tantalum (Ta), tungsten (W), or iridium (Ir).

[0059] It should be noted that the low acoustic impedance structures 131 and the high acoustic impedance structures 132 can have the same thickness or different thicknesses along the X-axis direction or the Y-axis direction. In addition, the materials forming each of the low acoustic impedance structures 131 can be the same or different, and the materials forming each of the high acoustic impedance structures 132 can be the same or different, which can be selected and set according to the needs of application scenarios.

[0060] Please continue to refer to FIG. 5, in the Bragg reflection structure 11 shown in FIG. 5, a plurality of layer structures arranged in the direction Z can be included. The plurality of layer structures can include at least one low acoustic impedance structure 111 and at least one high acoustic impedance structure 112. The Bragg reflection structure 11 is schematically shown in FIG. 5 to include three low acoustic impedance structures 111 and two high acoustic impedance structures 112, i.e. a five-layer structure. It can be understood that the Bragg reflection structure 11 can include more or fewer structures, which are arranged based on the needs of the scene, and the embodiments of the present application are not limited specifically. In the direction Z, the low acoustic impedance structure 111 and the high acoustic impedance structure 112 are alternately stacked. The low acoustic impedance structure can be formed of a low acoustic impedance material, which can include but is not limited to, for example, SiO2, SiN, Ti, or Al, etc.; the high acoustic impedance structure can be formed of a high acoustic impedance material, which can include but is not limited to, for example, AlN, AlScN, HfO2, HfN, WN, WO3, Ta2O5, Pt, Ta, W, or iridium Ir. In addition, the low acoustic impedance structure 111 and the high acoustic impedance structure 112 can have the same thickness or different thicknesses along the z-axis direction; in addition, the materials forming each low acoustic impedance structure 111 can be the same or different, and the materials forming each high acoustic impedance structure 112 can be the same or different, which are selected and arranged according to the needs of the application scenario.

[0061] Based on the structure of the bulk acoustic wave resonator 100 shown in FIGS. 4 to 6C, refer to FIGS. 7A and 7B, wherein both FIGS. 7A and 7B are Q value curves of the bulk acoustic wave resonator 100 provided by the embodiments of the present application and the Q value curves of the bulk acoustic wave resonator shown in FIG. 1 under the same area; wherein the area of the bulk acoustic wave resonator 100 in the comparison chart shown in FIG. 7A is larger than the area of the bulk acoustic wave resonator 100 in the comparison chart shown in FIG. 7B. In FIGS. 7A and 7B, the horizontal coordinate is frequency (unit: MHz), and the vertical coordinate is Q value; in addition, in FIGS. 7A and 7B, the solid line is the Q value curve of the bulk acoustic wave resonator 100 of the present application, and the dashed line is the Q value curve of the bulk acoustic wave resonator of the conventional structure shown in FIG. 1. It can be seen from FIGS. 7A and 7B that near the anti-resonance frequency as shown in FIG. 2, i.e. the frequency is near 5200 MHz, the Q value of the bulk acoustic wave resonator 100 provided by the embodiments of the present application is higher than the Q value of the bulk acoustic wave resonator shown in FIG. 1; in addition, at other frequencies, the Q value of the bulk acoustic wave resonator 100 provided by the embodiments of the present application is higher than the Q value of the bulk acoustic wave resonator shown in FIG. 1. It can be seen that the structure of the bulk acoustic wave resonator 100 provided by the embodiments of the present application, by setting the reflection structure 13, uses the reflection structure 13 to reflect the transverse leakage wave, to compensate for the problem that the ratio of the area of the resonator to the perimeter of the resonator is reduced, so as to reduce the energy leakage of the transverse leakage wave, improve the Q value of the bulk acoustic wave resonator, and thus the performance of the bulk acoustic wave resonator under various sizes can be improved.

[0062] The structure of the bulk acoustic resonator 100 provided by the embodiments of the present application is shown in FIGS. 4-6C. In the above embodiments, the structure of the bulk acoustic resonator 100 is an SMR structure. In a possible implementation, the structure of the bulk acoustic resonator 100 can also be an FBAR structure. Referring to FIG. 8, FIG. 8 is a structural schematic diagram of a bulk acoustic resonator 200 provided by an embodiment of the present application. As shown in FIG. 8, along the direction Z shown in FIG. 8, the bulk acoustic resonator 200 includes a substrate 10, and an electrode 122, a piezoelectric thin film layer 121, and an electrode 123 disposed on the substrate 10. In addition, a cavity structure 20 is disposed between the substrate 10 and the electrode 122, and the cavity structure 20 serves as a reflection layer of the bulk acoustic resonator 200. As shown in FIG. 8, the cavity structure 20 can be embedded in the substrate 10, close to one side of the electrode 122. The electrode 122 and the piezoelectric thin film layer 121 are disposed on the upper surface of the substrate 10. The electrode 122, the piezoelectric thin film layer 121, and the electrode 123 are the same as the electrode 122, the piezoelectric thin film layer 121, and the electrode 123 in the bulk acoustic resonator 100 shown in FIGS. 4 and 5, and reference is made to the related description, which will not be repeated here. The orthogonal projection of the electrode 123 onto the substrate 10 overlaps the cavity structure 20 in the x-axis and y-axis directions. Along the z-axis direction, the electrode 122, the cavity 20, and the piezoelectric thin film layer 121 and the electrode 123 aligned therewith in the x-axis and y-axis directions form a resonator working area. As shown in FIG. 8, the bulk acoustic resonator 200 further includes a reflection structure 13, which is disposed on the upper surface of the substrate 10 and embedded in the piezoelectric thin film layer 121. As can be seen from FIG. 8, the orthogonal projection of the cavity structure 20 onto the piezoelectric thin film layer 121 covers the piezoelectric thin film layer 121 and the reflection structure 13. In addition, the lower surface of the reflection structure 13 is in contact with the upper surface of the substrate 10, and the upper surface of the reflection structure 13 can be flush with the upper surface of the piezoelectric thin film layer 121 (i.e., the surface on which the electrode 123 is disposed) and exposed. The reflection structure 13 can be a Bragg reflection structure. When the reflection structure 13 is a Bragg reflection structure, the reflection structure 13 in the bulk acoustic resonator 200 is the same as the reflection structure 13 in the bulk acoustic resonator 100 shown in FIGS. 4-6C, and reference is made to the related description, which will not be repeated here.

[0063] It can be understood that the bulk acoustic resonator shown in the above embodiments can further include more or less structures. For example, in the bulk acoustic resonator 100 and the bulk acoustic resonator 200, a through hole penetrating the upper and lower surfaces of the piezoelectric thin film layer 121 is further arranged in the region of the piezoelectric thin film layer 121 where the electrodes 122 and the electrodes 123 are not arranged, and the through hole can be filled with a conductive material to form a conductor, so that the electrodes 122 covered by the piezoelectric thin film layer 121 can be led to the side of the piezoelectric thin film layer 121 away from the substrate 10 through the conductor in the through hole, so that the electrodes 122 and the electrodes 123 led to the upper surface of the piezoelectric thin film layer 121 can respectively lead out two ports to receive an externally applied voltage or be connected in series or parallel with other bulk acoustic resonators.

[0064] The above embodiments shown in FIGS. 4 to 6C and FIG. 8 show the structure of the bulk acoustic resonator provided by the embodiments of the present application. The structure of the bulk acoustic resonator provided by the embodiments of the present application can be prepared in various ways, for example, can include but is not limited to: an evaporation method or an etching method. The embodiments of the present application take the etching method as an example, and take the bulk acoustic resonator 100 shown in FIG. 5 as an example of the structure of the prepared bulk acoustic resonator, and describe the method for preparing the bulk acoustic resonator in combination with the process flow 900 shown in FIG. 9 and the structures in each process flow. As shown in FIG. 9, the process flow 900 of the method for preparing the bulk acoustic resonator includes steps 901 to 906.

[0065] In step 901, a substrate 10 is provided, and a Bragg reflection structure 11 is formed on the substrate 10.

[0066] In this step, the substrate 10 can be a semiconductor material, for example, silicon or the like. A low acoustic impedance material and a high acoustic impedance material are sequentially deposited on the substrate 10 to form a low acoustic impedance structure 111 and a high acoustic impedance structure 112 which are overlapped and stacked along the z direction. The low acoustic impedance material can include but is not limited to: SiO2, SiN, Ti or Al, etc.; and the high acoustic impedance material can include but is not limited to: AlN, AlScN, HfO2, HfN, WN, WO3, Ta2O5, Pt, Ta, W or Ir. The structure formed after this step is shown in FIG. 10A.

[0067] In step 902, a low acoustic impedance material is deposited on the Bragg reflection structure 11, and the low acoustic impedance material is etched by using a mask to form a low acoustic impedance structure 131 in the reflection structure 13.

[0068] In this step, a low acoustic impedance material can be deposited on the Bragg reflection structure 11, which can include but is not limited to SiO2, SiN, Ti or Al, etc. Then, based on the preset area for forming the piezoelectric thin film structure 12, the low acoustic impedance material is etched by using a patterned mask, wherein the part covered by the mask is reserved and the part not covered by the mask is etched, so as to form a low acoustic impedance structure 131 in the reflection structure 13 in the area of the Bragg reflection structure 11 where the piezoelectric thin film structure 12 is not arranged. The structure formed after this step is shown in FIG. 10B.

[0069] In step 903, a high acoustic impedance material is deposited on the Bragg reflection structure 11 in the area not covered by the low acoustic impedance structure 131, and the high acoustic impedance material is etched by using a mask, so as to form a high acoustic impedance structure 132 in the reflection structure 13.

[0070] In this step, a high acoustic impedance material can be deposited on the Bragg reflection structure 11, which can include but is not limited to AlN, AlScN, HfO2, HfN, WN, WO3, Ta2O5, Pt, Ta, W or Ir. Then, the high acoustic impedance material is etched by using a patterned mask. In the process of etching the high acoustic impedance material, the low acoustic impedance structure 131 needs to be protected to avoid being etched. Thus, the high acoustic impedance structure 132 in the reflection structure 13 is formed between every two low acoustic impedance structures 131 on the Bragg reflection structure 11. The structure formed after this step is shown in FIG. 10C.

[0071] In step 904, an electrode 122 is deposited on the Bragg reflection structure 11 in the area where the reflection structure 13 is not arranged. The electrode 122 is formed in the area enclosed by the reflection structure 13 and does not contact the reflection structure 13. The structure formed after this step is shown in FIG. 10D.

[0072] In step 905, a piezoelectric thin film layer 121 is formed on the Bragg reflection structure 11 and the electrode 122. The piezoelectric thin film layer 121 covers the electrode 122 and embeds the reflection structure 13 in the piezoelectric thin film layer 121. The structure formed after this step is shown in FIG. 10D.

[0073] In step 906, an electrode 123 is formed on the piezoelectric thin film layer 121.

[0074] After the above steps 901 to 906, the bulk acoustic wave resonator 100 shown in FIG. 5 can be prepared.

[0075] It should be noted that the present application is described in the embodiment of the preparation of the reflective structure 13 first, and then the electrode 122, the piezoelectric film layer 121 and the electrode 123. In addition, in the embodiment of the present application, when the reflective structure 13 is prepared, the low acoustic impedance structure 131 is prepared first, and then the high acoustic impedance structure 132 is prepared. In other possible implementations, the electrode 122, the piezoelectric film layer 121 and the electrode 123 can be prepared first, and then the reflective structure 13 is prepared. In addition, when the reflective structure 13 is prepared, the high acoustic impedance structure 132 can be prepared first, and then the low acoustic impedance structure 131 is prepared. The present application does not specifically limit the sequence of steps 902 to 906, which is set according to the needs of the scene.

[0076] The preparation method of the bulk acoustic wave resonator shown above shows that the reflective structure 13 is prepared on the Bragg reflection structure 11 by etching. In a possible implementation, the reflective structure 13 can also be prepared on the Bragg reflection structure 11 by evaporation. As shown in FIGS. 11A to 11F.

[0077] Step 1: Form a patterned first photoresist layer on the Bragg reflection structure 11, and the area of the Bragg reflection structure 11 without the first photoresist layer is used to form the low acoustic impedance structure 131. After this step, as shown in FIG. 11A.

[0078] Step 2: Form a low acoustic impedance material on the first photoresist layer and the Bragg reflection structure 11. After this step, as shown in FIG. 11B. As can be seen from FIG. 11B, the area of the Bragg reflection structure 11 without the first photoresist layer is provided with the low acoustic impedance material.

[0079] Step 3: Remove the first photoresist layer and the low acoustic impedance material provided on the first photoresist layer to form the low acoustic impedance structure 131. After this step, as shown in FIG. 11C.

[0080] Step 4: Form a patterned second photoresist layer on the Bragg reflection structure 11 and the low acoustic impedance structure 131, wherein the area of the Bragg reflection structure 11 between every two low acoustic impedance structures 131 is not provided with the photoresist material. After this step, as shown in FIG. 11D.

[0081] Step 5: Form a high acoustic impedance material on the second photoresist layer and the Bragg reflection structure 11. After this step, as shown in FIG. 11E.

[0082] Step 6: Remove the second photoresist layer and the high acoustic impedance material provided on the second photoresist layer to form the high acoustic impedance structure 132. After this step, as shown in FIG. 11F.

[0083] After the above steps 1 to step 6, the reflection structure 13 can be prepared on the Bragg reflection structure 11 by evaporation. In the embodiment of the application, the resonators are connected according to a certain topological structure to construct a frequency filter device, and therefore, the embodiment of the application further provides a specific filter. Please refer to FIG. 12, which is a structural schematic diagram of a filter 300 provided by the embodiment of the application. As shown in FIG. 12, the filter 300 includes an input terminal a, an output terminal b, a series branch S, and at least one parallel branch. The parallel branch P1 and the parallel branch P2 are schematically shown in FIG. 12. One end of the series branch S is connected to the input terminal a, and the other end is connected to the output terminal b. One end of the parallel branch P1 is connected to the series branch S, and the other end is grounded. One end of the parallel branch P2 is connected to the series branch S, and the other end is grounded. The parallel branch P2 is equivalent to being arranged in parallel with the parallel branch P1. The resonator 31 and the resonator 32 are arranged on the series branch S. The resonator 33 is arranged on the parallel branch P1. The resonator 34 is arranged on the parallel branch P2. At least one of the resonator 31, the resonator 32, the resonator 33, and the resonator 34 can adopt the structure of the resonator provided by the above embodiment (for example, shown in FIG. 4, FIG. 5, FIG. 6a to FIG. 6c, and FIG. 8). In a possible implementation manner, the resonator 31, the resonator 32, the resonator 33, and the resonator 34 all adopt the structure of the resonator provided by the above embodiment. It can be understood that more or fewer parallel branches can be included in FIG. 12, and more or fewer resonators can be included on the series branch. The resonators on the series branch and the resonators on the parallel branch can form more or fewer filter units. The embodiment of the application does not specifically limit the number of parallel branches, the number of series branches, and the number of resonators arranged on each branch included in the filter, and the number is set based on the needs of the scene. When the filter 300 includes more resonators, the more resonators can all select the structure of the resonator provided by the above embodiment.

[0084] The electronic device 400 can include a transceiver 401, a memory 402 and a processor 403. The transceiver 401 can be provided with the filter 300. The filter 300 can have the structure shown in FIG. 12. It should be understood that the electronic device 400 can be a terminal device such as a smartphone, a computer, a smart watch, etc. The terminal device can include a processor, a memory, a radio frequency circuit, an antenna, and an input / output device. The processor can be used to process communication protocols and communication data, control the entire smartphone, execute software programs, process data of the software programs, and support the smartphone to perform the actions described in the above method embodiments. The memory can be used to store software programs and data. The radio frequency circuit and the antenna can be collectively referred to as a transceiver, which can be used to receive and transmit radio frequency signals in the form of electromagnetic waves. The radio frequency circuit can be used to convert baseband signals into radio frequency signals and process the radio frequency signals. The radio frequency circuit can include the filter 300. The input / output device such as a touch screen, a display screen, a keyboard, etc. can be used to receive user input data and output data to the user.

[0085] When the smartphone is powered on, the processor can read the software programs in the memory, interpret and execute instructions of the software programs, and process data of the software programs. When data needs to be transmitted wirelessly, the processor can perform baseband processing on the data to be transmitted, output baseband signals to the radio frequency circuit, and the radio frequency circuit can perform radio frequency processing on the baseband signals and transmit radio frequency signals in the form of electromagnetic waves through the antenna. When data is transmitted to the smartphone, the radio frequency circuit can receive radio frequency signals through the antenna, convert the radio frequency signals into baseband signals, and output the baseband signals to the processor. The processor can convert the baseband signals into data and process the data.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and not to limit them. Although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can modify the technical solutions described in the above embodiments, or equivalently replace some or all of the technical features. Such modifications or replacements do not change the essence of the corresponding technical solutions.

Claims

1. A bulk acoustic wave resonator, characterized by, The application relates to a bulk acoustic wave resonator, comprising: a substrate; a first electrode, a piezoelectric thin film layer and a second electrode stacked on the substrate, the piezoelectric thin film layer being arranged between the first electrode and the second electrode and covering the first electrode; a first reflective structure arranged between the substrate and the piezoelectric thin film structure; a second reflective structure arranged on the substrate and embedded in the piezoelectric thin film layer.

2. The bulk acoustic resonator of claim 1, wherein, The first reflective structure is a first Bragg reflective structure stacked on the upper surface of the substrate; The first electrode is arranged on the upper surface of the first Bragg reflective structure.

3. The bulk acoustic resonator of claim 1, wherein, The first reflective structure is a first cavity structure embedded in the substrate and arranged on the side of the substrate close to the piezoelectric thin film structure; The first electrode is arranged on the upper surface of the substrate.

4. The bulk acoustic resonator of any one of claims 1 to 3, wherein, The second reflective structure is a second Bragg reflective structure comprising at least one layer of low acoustic impedance structure and at least one layer of high acoustic impedance structure, the at least one layer of low acoustic impedance structure and the at least one layer of high acoustic impedance structure being arranged alternately in a direction perpendicular to the stacking direction.

5. The bulk acoustic resonator of claim 4, wherein, The material of each layer of the at least one layer of low acoustic impedance structure comprises at least one of silicon dioxide, silicon nitride, titanium or aluminum.

6. The bulk acoustic resonator of claim 4, wherein, The material of each layer of the at least one layer of high acoustic impedance structure comprises at least one of aluminum nitride, scandium-doped aluminum nitride, hafnium dioxide, hafnium nitride, tungsten nitride, tungsten trioxide, tantalum pentoxide, platinum, tantalum, tungsten or iridium.

7. The bulk acoustic resonator of claim 4, wherein, The material of any layer of the at least one layer of high acoustic impedance structure satisfies the following condition: The compression wave acoustic impedance of the any layer of high acoustic impedance structure is greater than 0.5 times the compression wave acoustic impedance of the piezoelectric thin film layer.

8. The bulk acoustic resonator of claim 4, wherein, The material of any layer of the at least one layer of low acoustic impedance structure satisfies the following condition: The compression wave acoustic impedance of the any layer of low acoustic impedance structure is less than the shear wave acoustic impedance of the piezoelectric thin film layer.

9. A filter, characterized by The application relates to a filter, comprising an input terminal, an output terminal, a series branch and a parallel branch; One end of the series branch is connected to the input terminal, and the other end is connected to the output terminal; One end of the parallel branch is connected to the series branch, and the other end is grounded; The series branch comprises a first bulk acoustic wave resonator, and the parallel branch comprises a second bulk acoustic wave resonator; The first bulk acoustic wave resonator is as claimed in any one of claims 1 to 8, and the second bulk acoustic wave resonator is as claimed in any one of claims 1 to 8.

10. An electronic device, comprising: The application relates to a transceiver, comprising a filter as claimed in claim 9, a memory and a processor.

11. A method for fabricating a bulk acoustic wave resonator, characterized by, The application relates to a bulk acoustic wave resonator, comprising: providing a substrate; forming a first reflective structure on the substrate; sequentially forming a first electrode, a piezoelectric thin film layer and a second electrode on the first reflective structure, the piezoelectric thin film layer being arranged between the first electrode and the second electrode and covering the first electrode; forming a second reflective structure on the substrate, the second reflective structure being embedded in the piezoelectric thin film layer.

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