Bulk acoustic wave resonator and bulk acoustic wave filter based on inner and outer cycloid configuration

Abstract

The invention discloses a bulk acoustic wave resonator and a bulk acoustic wave filter based on inner and outer cycloid configurations, and belongs to the technical field of resonators, the bulk acoustic wave resonator comprises a substrate, a supporting layer, a bottom electrode, a piezoelectric layer and a top electrode which are sequentially stacked, and a cavity is formed between the substrate and the supporting layer; the contour shapes of the overlapped part of the bottom electrode and the piezoelectric layer and the overlapped part of the piezoelectric layer and the top electrode are symmetrical closed graphs, the closed graphs comprise hypocycloids and / or epicycloids, all the hypocycloids are obtained based on a first moving circle and a first fixed circle, and all the epicycloids are obtained based on a second moving circle and a second fixed circle. According to the bulk acoustic wave resonator based on the inner and outer cycloid configuration, the resonator can generate fewer vibration nodes, so that the energy loss is reduced, and the performance of the resonator is greatly improved.

Description

Technical Field

[0001] The invention belongs to the technical field of resonators, and in particular relates to a bulk acoustic wave resonator and a bulk acoustic wave filter based on an inner and outer cycloid configuration. Background Art

[0002] When the BAW resonator is working, it mainly uses the transmission of longitudinal sound waves to complete the conversion of electrical energy-mechanical energy-electrical energy. However, the existing resonator not only has a longitudinal transmission mode when working, but also a transverse mode, which will seriously affect the working performance of the resonator.

[0003] In order to suppress the generation of lateral modes, the prior art generally designs the resonator into a shape without parallel sides and right angles (the resonator shape specifically refers to the outline shape of the overlapping part of the bottom electrode and the piezoelectric layer and the overlapping part of the piezoelectric layer and the top electrode), such as a pentagon (see Appendix Figure 4 ), which aims to reduce parasitic effects by increasing the transmission distance of lateral waves.

[0004] However, the above shape still causes the resonator to produce more vibration nodes, resulting in partial energy loss, thereby causing the resonator performance (such as Q value) to decrease.

[0005] Therefore, the existing technology needs to be improved and developed. Summary of the invention

[0006] The object of the present invention is to provide a bulk acoustic wave resonator and a bulk acoustic wave filter based on an inner and outer cycloid configuration, which can make the resonator produce fewer vibration nodes, thereby reducing energy loss and greatly improving the performance of the resonator.

[0007] In a first aspect, the present invention provides a bulk acoustic wave resonator based on an inner and outer cycloid configuration, comprising a substrate, a supporting layer, a bottom electrode, a piezoelectric layer and a top electrode stacked in sequence, a cavity being arranged between the substrate and the supporting layer, the contour shapes of the overlapping portion of the bottom electrode and the piezoelectric layer and the overlapping portion of the piezoelectric layer and the top electrode are all symmetrical closed figures and the closed figures include inner and outer cycloids, all of the inner and outer cycloids are obtained based on a first moving circle and a first fixed circle, and all of the outer cycloids are obtained based on a second moving circle and a second fixed circle.

[0008] The BAW resonator based on the inner and outer cycloid configuration provided by the present invention has a shape of a symmetrical closed figure composed of inner and outer cycloids, and compared with the traditional pentagonal resonator, it can further suppress parasitic modes, thereby improving the resonator performance.

[0009] Furthermore, the hypocycloid includes at least two connected first arc segments, and a first protrusion with a smooth edge is provided at the intersection of the two connected first arc segments, and each of the first protrusions is symmetrical about a corresponding first symmetry axis, and the first symmetry axis passes through the vertex of the corresponding first protrusion; Take any two points on the first protrusion that are symmetrical about the first symmetry axis and use them as the first point and the second point respectively, the vector from the first point to the corresponding vertex of the first protrusion is used as the first vector, the vector from the second point to the corresponding vertex of the first protrusion is used as the second vector, and the angle between the first vector and the second vector is an obtuse angle.

[0010] The design optimizes the peak into a hypocycloid configuration of the first protrusion with a smooth edge, thereby improving the performance of the resonator and effectively reducing its processing difficulty.

[0011] Furthermore, the hypocycloid satisfies the following conditions: ; ; ; Wherein, a first rectangular coordinate system is established with the center of the first fixed circle as the first origin, is the x-axis coordinate value of the point on the hypocycloid in the first rectangular coordinate system, is the y-axis coordinate value of the point on the hypocycloid in the first rectangular coordinate system, is the angle between the line connecting the point on the hypocycloid with the first moving circle and the line connecting the point on the hypocycloid with the first fixed circle in the first rectangular coordinate system, is the radius of the first fixed circle, is the radius of the first moving circle, is the first real number preset, is the first parameter of the preset.

[0012] By adding the general hypocycloid parametric equation , thereby eliminating the peak on the general inner cycloid and forming a first protrusion with a smooth edge, thereby avoiding the peak from reducing the resonator performance and effectively reducing the processing difficulty.

[0013] Furthermore, the epicycloid includes at least two connected second arc segments, and a second protrusion with a smooth edge is provided at the intersection of the two connected second arc segments, and each of the second protrusions is symmetrical about a corresponding second symmetry axis, and the second symmetry axis passes through the vertex of the corresponding second protrusion; Any two points on the second protrusion that are symmetrical about the second symmetry axis are taken as the third point and the fourth point respectively, the vector from the third point to the corresponding vertex of the second protrusion is taken as the third vector, the vector from the fourth point to the corresponding vertex of the second protrusion is taken as the fourth vector, and the angle between the third vector and the fourth vector is an obtuse angle.

[0014] The design optimizes the peak into an epicycloid configuration of a second protrusion with a smooth edge, thereby improving the performance of the resonator and effectively reducing its processing difficulty.

[0015] Furthermore, the epicycloid satisfies the following conditions: ; ; ; Wherein, a second rectangular coordinate system is established with the center of the second fixed circle as the second origin. is the x-axis coordinate value of the point on the epicycloid in the second rectangular coordinate system, is the y-axis coordinate value of the point on the epicycloid in the second rectangular coordinate system, is the angle between the line connecting the point on the epicycloid with the second moving circle and the line connecting the point on the epicycloid with the second fixed circle in the second rectangular coordinate system, is the radius of the second fixed circle, is the radius of the second moving circle, is the preset second real number, The second parameter is preset.

[0016] Furthermore, projections of the outline shapes of the overlapping portion of the bottom electrode and the piezoelectric layer and the overlapping portion of the piezoelectric layer and the top electrode in the up-down direction completely overlap.

[0017] Furthermore, the overlapping portion of the bottom electrode and the piezoelectric layer and the overlapping portion of the piezoelectric layer and the top electrode have the same contour shape, and the overlapping portion of the bottom electrode and the piezoelectric layer and the overlapping portion of the piezoelectric layer and the top electrode decreases or increases in sequence.

[0018] Furthermore, the closed figure also includes straight lines and / or arcs or curves other than the hypocycloid and the epicycloid.

[0019] In a second aspect, the present invention provides a bulk acoustic wave filter, comprising the above-mentioned bulk acoustic wave resonator based on the hypocycloid configuration.

[0020] Furthermore, it includes a plurality of said inner and outer cycloid BAW resonators connected in series and / or a plurality of said inner and outer cycloid BAW resonators connected in parallel.

[0021] From the above, it can be seen that the bulk acoustic wave resonator based on the inner and outer cycloid configuration of the present invention has a more symmetrical shape of the resonator composed of the inner and outer cycloids. Compared with the existing pentagonal resonator, the resonator with a symmetrical structure will produce fewer vibration nodes, thereby reducing energy loss and greatly improving the Q value of the resonator. At the same time, the inner and outer cycloids can be directly obtained through a functional relationship, which is easier to design and has a smooth curve curvature, which helps to improve the problem of stress concentration, thereby optimizing and improving the performance of the resonator.

[0022] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or be understood by implementing the embodiments of the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic structural diagram of a bulk acoustic wave resonator based on an inner and outer cycloid configuration provided in an embodiment of the present invention.

[0024] Figure 2 It is a closed figure formed by the pentagonal hypocycloid in the embodiment of the present invention.

[0025] Figure 3 It is a closed figure formed by the pentagonal epicycloid in the embodiment of the present invention.

[0026] Figure 4 FIG. 1 is a schematic diagram of the structure of a filter using a pentagonal resonator in the prior art.

[0027] Figure 5 It is a closed figure of a general pentagonal hypocycloid in an embodiment of the present invention.

[0028] Figure 6 It is a closed figure of a general pentagonal epicycloid in an embodiment of the present invention.

[0029] Figure 7 It is a top view of a resonator in which the outline sizes of the support layer, the bottom electrode, the piezoelectric layer and the top electrode are successively reduced inwards in an embodiment of the present invention.

[0030] Figure 8 It is a closed figure including a hypocycloid and a straight line in one embodiment of the present invention.

[0031] Fig. 9 It is a closed figure including a hypocycloid and an arc in one embodiment of the present invention.

[0032] Fig.10 It is a closed figure including a hypocycloid and a curve in one embodiment of the present invention.

[0033] Fig.11 It is a closed figure including a hypocycloid and an epicycloid in one embodiment of the present invention.

[0034] Fig.12 A schematic diagram of the structure of a bulk acoustic wave filter provided by an embodiment of the present invention.

[0035] Description of labels: 100, substrate; 200, supporting layer; 300, bottom electrode; 400, piezoelectric layer; 500, top electrode; 600, cavity; 710, inner cycloid; 711, first arc segment; 712, first protrusion; 720, outer cycloid; 721, second arc segment; 722, second protrusion; 730, peak. DETAILED DESCRIPTION

[0036] The embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0037] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "multiple" is two or more, unless otherwise clearly and specifically defined.

[0038] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection, an electrical connection, or mutual communication; it can be a direct connection, or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0039] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0040] The disclosure below provides many different embodiments or examples to implement different structures of the present invention. In order to simplify the disclosure of the present invention, the parts and settings of specific examples are described below. Of course, they are only examples, and the purpose is not to limit the present invention. In addition, the present invention can repeat reference numbers and / or reference letters in different examples, and this repetition is for the purpose of simplicity and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed. In addition, the present invention provides various specific examples of processes and materials, but those of ordinary skill in the art can appreciate the application of other processes and / or the use of other materials.

[0041] Reference Figure 1 , Attachment Figure 2 , Attachment Figure 3 and attached Fig.11 The present invention provides a bulk acoustic wave resonator based on an inner and outer cycloid configuration, comprising a substrate 100, a support layer 200, a bottom electrode 300, a piezoelectric layer 400 and a top electrode 500 stacked in sequence, a cavity 600 is arranged between the substrate 100 and the support layer 200, the contour shapes of the overlapping part of the bottom electrode 300 and the piezoelectric layer 400 and the overlapping part of the piezoelectric layer 400 and the top electrode 500 are all symmetrical closed figures, and the closed figures include inner cycloids 710 and / or outer cycloids 720, all inner cycloids 710 are obtained based on a first moving circle and a first fixed circle, and all outer cycloids 720 are obtained based on a second moving circle and a second fixed circle.

[0042] In this embodiment, the symmetrical closed figure based on the configuration of the inner cycloid 710 and the outer cycloid 720 can greatly reduce the complexity of the vibration characteristics of the resonator and avoid the formation of asymmetric vibration modes due to its symmetry, so it can avoid the unpredictable behavior of the resonator and reduce the generation of vibration nodes, thereby reducing energy loss and achieving the effect of improving the stability of the resonator. In addition, the various different resonant modes (i.e., waves of different frequencies) generated by the internal waves of the resonator will cancel each other out at the geometric center of the resonator, thereby greatly suppressing parasitic modes, reducing parasitic effects and avoiding energy leakage, so that the device has a higher Q value. At the same time, the vibration of the resonator can be modeled by a simpler linear differential equation, thereby reducing the difficulty of analyzing and understanding its vibration behavior. Further, the inner cycloid 710 and the outer cycloid 720 can be directly obtained through a functional relationship. In addition to being easy to design, relying on its smooth curves can also help improve the problem of stress concentration, thereby optimizing and improving the performance of the resonator.

[0043] In certain embodiments, referring to Figure 1 and attached Figure 5 The hypocycloid 710 includes at least two connected first arc segments 711, and a first protrusion 712 with smooth edges (smooth edges means no sharp edges) is provided at the intersection of the two connected first arc segments 711. Each first protrusion 712 is symmetrical about a corresponding first symmetry axis, and the first symmetry axis passes through the vertex of the corresponding first protrusion 712; Any two points on the first protrusion 712 that are symmetrical about the first symmetry axis are taken as the first point and the second point respectively, the vector from the first point to the corresponding vertex of the first protrusion 712 is taken as the first vector, the vector from the second point to the corresponding vertex of the first protrusion 712 is taken as the second vector, and the angle between the first vector and the second vector is an obtuse angle.

[0044] Generally, the hypocycloid 710 has a sharp peak 730, which often easily causes the resonator to generate clutter and reduce the resonator performance, and also increases the difficulty of processing. In this regard, this embodiment softens the peak 730 and reflects it in the modification of the hypocycloid 710, and finally designs a hypocycloid configuration in which the peak 730 is optimized to a first protrusion 712 with a smooth edge, thereby improving the resonator performance and effectively reducing its processing difficulty.

[0045] Specifically, the hypocycloid 710 satisfies the following conditions: Formula 1; ; ; Among them, the first rectangular coordinate system is established with the center of the first fixed circle as the first origin. is the x-axis coordinate value of the point on the hypocycloid in the first rectangular coordinate system, is the y-axis coordinate value of the point on the hypocycloid in the first rectangular coordinate system, is the angle between the line connecting the point on the hypocycloid with the first moving circle and the line connecting the point on the hypocycloid with the first fixed circle in the first rectangular coordinate system, is the radius of the first fixed circle, is the radius of the first moving circle, is the first real number preset, is the first parameter of the preset.

[0046] Specifically, the coordinates of the first point are , the coordinates of the second point are , the vertex coordinates of the first protrusion 712 are marked as , the first vector and the second vector can be calculated according to the following formula: ; in, is the first vector, is the second vector.

[0047] The angle between the first and second vectors is then calculated according to the following formula: (Formula 2); in, is the angle between the first vector and the second vector.

[0048] Reference Figure 2 and attached Figure 5 , the following will be explained in detail in combination with actual experimental data: The following are the parametric equations for a general hypocycloid: (Formula 3); when When it is an integer, according to Formula 3, the total number of hypocycloids 710 surrounding the closed figure is There are 730 peaks, among which, when When ( is a preset natural number, is expressed as a natural number), the vertex coordinates of the peak 730 can be obtained and recorded as , and then the vertex coordinates of the peak 730 are regarded as the vertex coordinates of the first protrusion 712 (i.e. ),Pick ,Pick , and substitute it into formula 2, we can calculate Obviously, at this time It is an acute angle and does not meet the design requirements of the resonator.

[0049] The present invention obtains the same hypocycloid 710 according to Formula 1, and substitutes the same parameters into Formula 2 to calculate: ,at this time It is corrected to an obtuse angle, which meets the design requirements of the resonator.

[0050] In this embodiment, by adding , thereby eliminating the peak 730 on the general inner cycloid and forming a first protrusion 712 with a smooth edge, thereby preventing the peak 730 from reducing the resonator performance and effectively reducing the processing difficulty.

[0051] It should be noted that The value of directly affects the corrected angle, so The value of needs to be set according to the actual design requirements of the resonator.

[0052] In certain embodiments, referring to Figure 3 and attached Figure 6 The epicycloid 720 includes at least two connected second arc segments 721, and a second protrusion 722 with a smooth edge is provided at the intersection of the two connected second arc segments 721, and each second protrusion 722 is symmetrical about a corresponding second symmetry axis, and the second symmetry axis passes through the vertex of the corresponding second protrusion 722; Any two points on the second protrusion 722 that are symmetrical about the second symmetry axis are taken as the third point and the fourth point respectively, the vector from the third point to the corresponding vertex of the second protrusion 722 is taken as the third vector, the vector from the fourth point to the corresponding vertex of the second protrusion 722 is taken as the fourth vector, and the angle between the third vector and the fourth vector is an obtuse angle.

[0053] Generally, the epicycloid 720 has a sharp peak 730, which often easily causes the resonator to generate clutter and reduce the resonator performance, and also increases the difficulty of processing. In this regard, this embodiment softens the peak 730 and reflects it in the modification of the epicycloid 720, and finally designs an epicycloid configuration that optimizes the peak 730 to a second protrusion 722 with a smooth edge, thereby improving the resonator performance and effectively reducing its processing difficulty.

[0054] In some embodiments, the epicycloid 720 satisfies the following conditions: (Formula 4); ; ; Among them, the second rectangular coordinate system is established with the center of the second fixed circle as the second origin. is the x-axis coordinate value of the point on the epicycloid in the second rectangular coordinate system, is the y-axis coordinate value of the point on the epicycloid in the second rectangular coordinate system, is the angle between the line connecting the point on the epicycloid with the second moving circle and the line connecting the point on the epicycloid with the second fixed circle in the second rectangular coordinate system, is the radius of the second fixed circle, is the radius of the second moving circle, is the preset second real number, The second parameter is preset.

[0055] Specifically, the coordinates of the third point are , the coordinates of the fourth point are , the vertex coordinates of the second protrusion 722 are marked as , the third and fourth vectors can be calculated according to the following formula: ; in, is the third vector, is the fourth vector.

[0056] The angle between the third and fourth vectors is then calculated according to the following formula: (Formula 5); in, is the angle between the third vector and the fourth vector.

[0057] Reference Figure 3 and attached Figure 6 , the following will be explained in detail in combination with actual experimental data: The following are the parametric equations for a general hypocycloid: (Formula 6); when When it is an integer, according to Formula 6, there are a total of There are 730 peaks, among which, when When , the vertex coordinates of the peak 730 can be obtained and recorded as , and then the vertex coordinates of the peak 730 are regarded as the vertex coordinates of the second protrusion 722 (i.e. ),Pick ,Pick , and substitute it into Formula 5, we can calculate Obviously, at this time It is an acute angle and does not meet the design requirements of the resonator.

[0058] The present invention obtains the same epicycloid 720 according to Formula 4, and substitutes the same parameters into Formula 5 to calculate: ,at this time It is corrected to an obtuse angle, which meets the design requirements of the resonator.

[0059] In this embodiment, by adding , thereby eliminating the peak 730 on the general epicycloid and forming a second protrusion 722 with a smooth edge, thereby preventing the peak 730 from reducing the resonator performance and effectively reducing the processing difficulty.

[0060] It should be noted that The value of directly affects the corrected angle, so The value of needs to be set according to the actual design requirements of the resonator.

[0061] In some embodiments, the projections of the contour shapes of the overlapping portions of the bottom electrode 300 and the piezoelectric layer 400 and the overlapping portions of the piezoelectric layer 400 and the top electrode 500 in the upper and lower directions completely overlap, and the contour shapes and sizes of the bottom electrode 300, the piezoelectric layer 400 and the top electrode 500 are the same, which makes them easier to process and their processing costs are relatively lower.

[0062] In certain embodiments, referring to Figure 7 The overlapping portion of the bottom electrode 300 and the piezoelectric layer 400 and the overlapping portion of the piezoelectric layer 400 and the top electrode 500 have the same contour shape, and the overlapping portion of the bottom electrode 300 and the piezoelectric layer 400 and the overlapping portion of the piezoelectric layer 400 and the top electrode 500 decreases or increases in sequence.

[0063] For example, the outline sizes of the supporting layer 200, the bottom electrode 300, the piezoelectric layer 400 and the top electrode 500 decrease inward in sequence, and the outline line of the bottom electrode 300 is located within the outline line of the supporting layer 200, the outline line of the piezoelectric layer 400 is located within the outline line of the bottom electrode 300, and the outline line of the top electrode 500 is located within the outline line of the piezoelectric layer 400, but the overlapping part of the bottom electrode 300 and the piezoelectric layer 400 and the downward projection of the overlapping part of the piezoelectric layer 400 and the top electrode 500 along the up and down directions all fall within the outline line of the supporting layer 200.

[0064] In certain embodiments, referring to Figure 8 , Attachment Fig. 9 and attached Fig.10 The closed figure also includes straight lines and / or arcs or curves other than the inner cycloid 710 and the outer cycloid 720 .

[0065] In this embodiment, the closed figure is not limited to being composed of only the hypocycloid 710 and / or the epicycloid 720. Straight lines, arcs and curves can be introduced without destroying the symmetry of the closed figure, which can also suppress parasitic modes to a certain extent.

[0066] In some embodiments, the substrate 100 is made of any one of Si, SiO2, SiC, sapphire, LiGaO2, and a metal element; The support layer 200 is made of any one of AlN, SiO2, SiC, and Si3N4; The bottom electrode 300 and the top electrode 500 are respectively made of any one of Al, Mo, W, Pt, Ti, Au, and Ru; The piezoelectric layer 400 is made of any one of single crystal AlN, polycrystalline AlN, ZnO, PZT, LiNbO 3 , LiTaO 3 , and BST.

[0067] The present invention provides a bulk acoustic wave filter, comprising the bulk acoustic wave resonator based on the epicycloid configuration in the above embodiment.

[0068] In certain embodiments, referring to Fig.12 The BAW filter includes a plurality of BAW resonators of inner and outer cycloid configuration connected in series and / or a plurality of BAW resonators of inner and outer cycloid configuration connected in parallel.

[0069] In the description of this specification, the description with reference to the terms "one embodiment", "certain embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0070] The above are only some embodiments of the present invention. For those skilled in the art, several modifications and improvements can be made without departing from the creative concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A bulk acoustic wave resonator based on an inner and outer cycloid configuration, characterized in that: The invention comprises a substrate (100), a support layer (200), a bottom electrode (300), a piezoelectric layer (400) and a top electrode (500) which are stacked in sequence, wherein a cavity (600) is provided between the substrate (100) and the support layer (200), and is characterized in that the contour shapes of the overlapping portion of the bottom electrode (300) and the piezoelectric layer (400) and the overlapping portion of the piezoelectric layer (400) and the top electrode (500) are both symmetrical closed figures, and the closed figures include hypocycloids (710) and / or epicycloids (720), all of the hypocycloids (710) are obtained based on a first moving circle and a first fixed circle, and all of the epicycloids (720) are obtained based on a second moving circle and a second fixed circle.

2. The BAW resonator based on the epicycloid configuration according to claim 1, characterized in that: The hypocycloid (710) comprises at least two connected first arc segments (711), a first protruding portion (712) with a smooth edge is provided at the intersection of the two connected first arc segments (711), each first protruding portion (712) is symmetrical about a corresponding first symmetry axis, and the first symmetry axis passes through the vertex of the corresponding first protruding portion (712); Any two points on the first protrusion (712) that are symmetrical about the first symmetry axis are taken as the first point and the second point respectively, a vector from the first point to the corresponding vertex of the first protrusion (712) is taken as the first vector, a vector from the second point to the corresponding vertex of the first protrusion (712) is taken as the second vector, and an angle between the first vector and the second vector is an obtuse angle.

3. The bulk acoustic wave resonator based on the epicycloid configuration according to claim 2, characterized in that: The hypocycloid (710) satisfies the following conditions: ； ； ； Wherein, a first rectangular coordinate system is established with the center of the first fixed circle as the first origin, is the x-axis coordinate value of the point on the hypocycloid in the first rectangular coordinate system, is the y-axis coordinate value of the point on the hypocycloid in the first rectangular coordinate system, is the angle between the line connecting the point on the hypocycloid with the first moving circle and the line connecting the point on the hypocycloid with the first fixed circle in the first rectangular coordinate system, is the radius of the first fixed circle, is the radius of the first moving circle, is the first real number preset, is the first parameter of the preset.

4. The BAW resonator based on the epicycloid configuration according to claim 1, characterized in that: The epicycloid (720) comprises at least two connected second arc segments (721), a second protruding portion (722) with a smooth edge is provided at the intersection of the two connected second arc segments (721), each second protruding portion (722) is symmetrical about a corresponding second symmetry axis, and the second symmetry axis passes through the vertex of the corresponding second protruding portion (722); Any two points on the second protrusion (722) that are symmetrical about the second symmetry axis are taken as the third point and the fourth point respectively, a vector from the third point to the corresponding vertex of the second protrusion (722) is taken as the third vector, a vector from the fourth point to the corresponding vertex of the second protrusion (722) is taken as the fourth vector, and the angle between the third vector and the fourth vector is an obtuse angle.

5. The BAW resonator based on the epicycloid configuration according to claim 4, characterized in that: The epicycloid (720) satisfies the following conditions: ； ； ； Wherein, a second rectangular coordinate system is established with the center of the second fixed circle as the second origin. is the x-axis coordinate value of the point on the epicycloid in the second rectangular coordinate system, is the y-axis coordinate value of the point on the epicycloid in the second rectangular coordinate system, is the angle between the line connecting the point on the epicycloid with the second moving circle and the line connecting the point on the epicycloid with the second fixed circle in the second rectangular coordinate system, is the radius of the second fixed circle, is the radius of the second moving circle, is the preset second real number, The second parameter is preset.

6. The BAW resonator based on the epicycloid configuration according to claim 1, characterized in that: The projections of the outline shapes of the overlapping portion of the bottom electrode (300) and the piezoelectric layer (400) and the overlapping portion of the piezoelectric layer (400) and the top electrode (500) in the up and down directions completely overlap.

7. The BAW resonator based on the epicycloid configuration according to claim 1, characterized in that: The contour shapes of the overlapping parts of the bottom electrode (300) and the piezoelectric layer (400) and the overlapping parts of the piezoelectric layer (400) and the top electrode (500) are the same, and the contour sizes of the overlapping parts of the bottom electrode (300) and the piezoelectric layer (400) and the overlapping parts of the piezoelectric layer (400) and the top electrode (500) decrease or increase in sequence.

8. The BAW resonator based on the epicycloid configuration according to claim 1, characterized in that: The closed figure also includes straight lines and / or arcs or curves other than the hypocycloid (710) and the epicycloid (720).

9. A bulk acoustic wave filter, characterized in that: The invention comprises a bulk acoustic wave resonator based on an inner and outer cycloid configuration as claimed in any one of claims 1 to 8.

10. The bulk acoustic wave filter according to claim 9, characterized in that It comprises a plurality of said inner and outer cycloid-shaped BAW resonators connected in series and / or a plurality of said inner and outer cycloid-shaped BAW resonators connected in parallel.

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