Bulk acoustic wave resonator

Abstract

This invention discloses a bulk acoustic wave resonator. The resonator includes an upper electrode, a piezoelectric layer, and a lower electrode, with the piezoelectric layer disposed between the upper and lower electrodes. At least a portion of the boundary of the piezoelectric layer's vertical projection onto the lower electrode includes multiple serrated structures. By providing multiple serrated structures on the side of the piezoelectric layer, irregular edges are formed on its side surface. This allows the transverse bulk acoustic waves generated after the piezoelectric layer is energized to undergo random or diffuse reflection when propagating to the surface of the piezoelectric layer in contact with air, preventing the formation of transverse standing waves. This invention solves the problem that existing bulk acoustic wave resonators, in addition to generating longitudinal bulk acoustic waves, also generate other forms of standing waves, increasing the noise of the bulk acoustic wave resonator and adversely affecting its performance. By preventing the generation of other forms of standing waves, reducing the noise of the bulk acoustic wave resonator, and improving its performance, this invention improves the performance of the bulk acoustic wave resonator.

Description

Technical Field

[0001] This invention relates to the field of resonator technology, and more particularly to a bulk acoustic resonator. Background Technology

[0002] An ideal bulk acoustic resonator is an acoustic stack consisting of an upper electrode, a piezoelectric layer, and a lower electrode. This resonator has advantages such as small size, good performance, and suitability for integrated circuits.

[0003] Bulk acoustic wave (BAS) resonators typically excite longitudinal bulk acoustic waves propagating along the thickness of the piezoelectric layer. These longitudinal BAS waves are the main factor affecting the quality of BAS resonators. However, in addition to generating the desired longitudinal BAS waves, existing BAS resonators often generate other forms of standing waves in the device, increasing the noise of the BAS resonator and adversely affecting its performance. Summary of the Invention

[0004] This invention provides a bulk acoustic wave resonator to prevent the generation of other forms of standing waves, reduce the noise of the bulk acoustic wave resonator, and improve the performance of the bulk acoustic wave resonator.

[0005] In a first aspect, embodiments of the present invention provide a bulk acoustic resonator, the bulk acoustic resonator comprising:

[0006] An upper electrode, a piezoelectric layer, and a lower electrode, wherein the piezoelectric layer is disposed between the upper electrode and the lower electrode;

[0007] The boundary of the piezoelectric layer in the vertical projection of the lower electrode includes at least a plurality of serrated structures.

[0008] Optionally, at least a portion of the boundary of the vertical projection of the upper electrode and the lower electrode onto a plane perpendicular to the thickness direction of the bulk acoustic resonator includes a plurality of sawtooth structures.

[0009] Optionally, the center-to-center distance between adjacent sawtooth structures is greater than or equal to 2 micrometers.

[0010] Optionally, all boundaries of the piezoelectric layer in the vertical projection of the lower electrode include multiple serrated structures.

[0011] Optionally, multiple serrated structures are connected end-to-end on the boundary.

[0012] Optionally, the serrated structure may be triangular or trapezoidal in shape.

[0013] Optionally, the shape of the bulk acoustic resonator's vertical projection onto a plane perpendicular to its thickness direction includes a polygon.

[0014] Optionally, the upper electrode and the lower electrode are made of any one of gold, molybdenum, aluminum, chromium and nickel.

[0015] Optionally, the piezoelectric layer is made of any one of lead zirconate titanate piezoelectric ceramic, zinc oxide, and aluminum nitride.

[0016] This invention provides a bulk acoustic wave resonator, comprising an upper electrode, a piezoelectric layer, and a lower electrode, wherein the piezoelectric layer is disposed between the upper and lower electrodes; at least a portion of the boundary of the piezoelectric layer in the vertical projection of the lower electrode includes multiple serrated structures. By providing multiple serrated structures on the side of the piezoelectric layer, irregular edges are formed on the side of the piezoelectric layer, so that when the transverse bulk acoustic wave generated after the piezoelectric layer is energized propagates to the surface of the piezoelectric layer in contact with air, disordered reflection or diffuse reflection can occur, preventing the formation of transverse standing waves. This solves the problem that existing bulk acoustic wave resonators, in addition to generating longitudinal bulk acoustic waves, also generate other forms of standing waves, increasing the noise of the bulk acoustic wave resonator and adversely affecting its performance. By preventing the generation of other forms of standing waves, reducing the noise of the bulk acoustic wave resonator, and improving its performance, this invention improves the performance of the bulk acoustic wave resonator. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of a planar structure of a bulk acoustic resonator provided in an embodiment of the present invention;

[0018] Figure 2 This is a three-dimensional structural schematic diagram of a bulk acoustic resonator provided in an embodiment of the present invention;

[0019] Figure 3 This is a vertical projection schematic diagram of a bulk acoustic resonator provided in an embodiment of the present invention;

[0020] Figure 4 This is a schematic diagram of a planar structure of a bulk acoustic resonator in the prior art;

[0021] Figure 5 This is a three-dimensional structural schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention;

[0022] Figure 6 This is a schematic diagram of the impedance and frequency function curves of a bulk acoustic resonator provided in an embodiment of the present invention;

[0023] Figure 7-15 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention;

[0024] Figure 16 This is a schematic diagram of the impedance and frequency function curves of another bulk acoustic resonator provided in an embodiment of the present invention;

[0025] Figure 17-18 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention. Detailed Implementation

[0026] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0027] Figure 1 This is a schematic diagram of a planar structure of a bulk acoustic resonator provided in an embodiment of the present invention, specifically showing the planar side view structure of the bulk acoustic resonator; Figure 2 This is a three-dimensional structural schematic diagram of a bulk acoustic resonator provided in an embodiment of the present invention, specifically showing the three-dimensional side view structure of the bulk acoustic resonator; Figure 3 This is a vertical projection schematic diagram of a bulk acoustic resonator provided in an embodiment of the present invention. Figure 3 It schematically shows, as Figure 1-2 The vertical projection shape of the piezoelectric layer 2 on the lower electrode 3 in the bulk acoustic resonator shown. Figure 1-3 As shown, the bulk acoustic resonator includes: an upper electrode 1, a piezoelectric layer 2, and a lower electrode 3, with the piezoelectric layer 2 disposed between the upper electrode 1 and the lower electrode 3; at least a portion of the boundary of the piezoelectric layer 2 in the vertical projection of the lower electrode 3 includes a plurality of sawtooth structures A.

[0028] like Figure 1-2 As shown, the bulk acoustic resonator provided in this embodiment can be based on the resonance technology of bulk acoustic waves, applying the piezoelectric effect. After being connected to an external power supply, the electrical energy signal is converted into a corresponding acoustic wave signal to form resonance. Specifically, the upper electrode 1 can be connected to one pole of the external power supply, and the lower electrode 3 can be connected to the other pole of the external power supply. After being energized, the piezoelectric layer 2 will undergo corresponding expansion or contraction deformation as the electric field generated by the external power supply changes, thereby generating longitudinal bulk acoustic waves in the thickness direction of the piezoelectric layer 2. When the longitudinal bulk acoustic waves propagate to the interface between the upper electrode 1 and the air and the interface between the lower electrode 3 and the air, they can be reflected, thereby forming oscillations in the piezoelectric layer 2.

[0029] like Figure 1-3 As shown, multiple sawtooth structures can be provided on the side of the piezoelectric layer 2 along the thickness direction ao, so that the side of the piezoelectric layer 2 forms an irregular edge. When the piezoelectric layer 2 is vertically projected onto the lower electrode 3 along the thickness direction ao, the vertical projection on the surface of the lower electrode 3 presents a shape that is consistent with the shape of the side edge of the piezoelectric layer 2, including at least a portion of the boundary including multiple sawtooth structures A.

[0030] Figure 4 This is a schematic diagram of a planar structure of a bulk acoustic wave resonator in the prior art, specifically showing the planar side view structure of the bulk acoustic wave resonator in the prior art. For example... Figure 4As shown, in the prior art, the piezoelectric layer 2' of the bulk acoustic wave resonator has the same size and shape as the upper electrode 1' and the lower electrode 3'. The side of the piezoelectric layer 2' has a regular planar structure, and all edges are straight lines. However, when the prior art bulk acoustic wave resonator is connected to an external power source, in addition to the desired longitudinal bulk acoustic wave, transverse bulk acoustic waves are also generated in the piezoelectric layer 2'. After standing waves are formed, the noise of the bulk acoustic wave resonator is increased, and the performance of the bulk acoustic wave resonator is reduced.

[0031] The bulk acoustic wave resonator provided in this embodiment includes an upper electrode, a piezoelectric layer, and a lower electrode, with the piezoelectric layer disposed between the upper and lower electrodes. At least a portion of the boundary of the piezoelectric layer's vertical projection onto the lower electrode includes multiple serrated structures. By providing multiple serrated structures on the side of the piezoelectric layer, irregular edges are formed on the side of the piezoelectric layer. This allows the transverse bulk acoustic waves generated after the piezoelectric layer is energized to undergo disordered reflection or diffuse reflection when they propagate to the surface of the piezoelectric layer in contact with air, preventing the formation of transverse standing waves. This solves the problem that existing bulk acoustic wave resonators, in addition to generating longitudinal bulk acoustic waves, also generate other forms of standing waves, increasing the noise of the bulk acoustic wave resonator and adversely affecting its performance. By preventing the generation of other forms of standing waves, reducing the noise of the bulk acoustic wave resonator, and improving its performance, this embodiment addresses the issue of existing bulk acoustic wave resonators generating other forms of standing waves, increasing the noise of the bulk acoustic wave resonator, and improving its performance.

[0032] Figure 5 This is a three-dimensional structural schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention. Figure 5 As shown, optionally, based on the above technical solution, at least a portion of the boundary of the vertical projection of the upper electrode 1 and the lower electrode 3 onto a plane perpendicular to the thickness direction of the bulk acoustic resonator includes a plurality of sawtooth structures A.

[0033] Specifically, refer to Figure 5 Multiple sawtooth structures A can be provided on the sides of the upper electrode 1, piezoelectric layer 2, and lower electrode 3, so that the sides of the upper electrode 1, piezoelectric layer 2, and lower electrode 3 all form irregular edges. When the upper electrode 1, piezoelectric layer 2, and lower electrode 3 are vertically projected along the thickness direction ao of the bulk acoustic resonator, the vertical projection shows a shape that is consistent with the shape of the side edges of the upper electrode 1, piezoelectric layer 2, and lower electrode 3, including at least a portion of the boundary containing multiple sawtooth structures A (the specific shape of the vertical projection can be referenced). Figure 3 When the bulk acoustic wave resonator is connected to an external power source, the bulk acoustic waves generated in the piezoelectric layer 2 in directions other than the longitudinal bulk acoustic waves, such as the transverse bulk acoustic waves, will propagate in the piezoelectric layer 2. The surfaces of the multiple sawtooth sides of the upper electrode 1, piezoelectric layer 2, and lower electrode 3 that are in contact with the air will undergo more disordered reflections or diffuse reflections. This prevents the formation of transverse standing waves or standing waves in other directions, further reducing the noise of the bulk acoustic wave resonator and improving its performance.

[0034] It should be noted that, Figure 5 The illustration shows the case where the upper electrode 1, piezoelectric layer 2, and lower electrode 3 have the same shape. In actual applications, the upper electrode 1, piezoelectric layer 2, and lower electrode 3 may have the same or different shapes. As long as the upper electrode 1, piezoelectric layer 2, and lower electrode 3 can form serrated sides, the embodiments of the present invention do not impose any restrictions on this.

[0035] Figure 6 This is a schematic diagram of the impedance and frequency function curves of a bulk acoustic resonator provided in an embodiment of the present invention. Figure 6 As shown, curve C, indicated by the dashed line, is... Figure 4 The provided prior art provides a function curve of impedance versus frequency for a bulk acoustic resonator, where curve D is... Figure 5 The impedance-frequency function curve of the bulk acoustic wave resonator provided in the embodiment of the present invention is shown. According to the functional relationship between impedance and frequency of the bulk acoustic wave resonator, the smoother the curve, the less noise the bulk acoustic wave resonator has. Therefore, the bulk acoustic wave resonator including sawtooth structure A provided in the embodiment of the present invention has less noise and better device performance compared with the prior art.

[0036] refer to Figure 3 Optionally, based on the above technical solution, all boundaries of the piezoelectric layer's vertical projection onto the lower electrode include multiple sawtooth structures A. For example, when sawtooth structures A are provided only on the sides of the piezoelectric layer, multiple sawtooth structures A can be provided on all sides of the piezoelectric layer; correspondingly, all boundaries of the piezoelectric layer's vertical projection onto the lower electrode include multiple sawtooth structures A. When sawtooth structures A are provided on the sides of the upper electrode, piezoelectric layer, and lower electrode, multiple sawtooth structures A can be provided on all sides of the upper electrode, piezoelectric layer, and lower electrode; correspondingly, when the upper electrode, piezoelectric layer, and lower electrode are vertically projected along the thickness direction of the bulk acoustic resonator, all boundaries of the vertical projection include multiple sawtooth structures A.

[0037] Optionally, based on the above technical solution, the boundary of the piezoelectric layer in the vertical projection of the lower electrode includes multiple sawtooth structures. Specifically, any one boundary may include multiple sawtooth structures, any two boundaries may include multiple sawtooth structures, or any three boundaries may include multiple sawtooth structures. Figure 7 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention. Figure 7 The diagram schematically illustrates a case where the boundary of the piezoelectric layer's vertical projection onto the lower electrode includes multiple sawtooth structures A. Figure 8 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention; Figure 9 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention. Figure 8-9The diagram schematically illustrates two cases where the two boundaries of the piezoelectric layer in the vertical projection of the lower electrode include multiple sawtooth structures A. Figure 10 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention. Figure 10 The diagram schematically illustrates the case where the three boundaries of the piezoelectric layer in the vertical projection of the lower electrode include multiple sawtooth structures A.

[0038] It should be noted that if a sawtooth structure is provided on the sides of the upper electrode, piezoelectric layer, and lower electrode of the bulk acoustic wave resonator, the shape of the vertical projection of the upper electrode, piezoelectric layer, and lower electrode along the thickness direction of the bulk acoustic wave resonator can also be referenced. Figure 3 ,as well as Figure 7-10 The specific choice is whether to set the sawtooth structure A only in the piezoelectric layer, or to set the sawtooth structure A in the upper electrode, the piezoelectric layer and the lower electrode, and the arrangement of the sawtooth structure A on each side in both cases, which can be determined based on the actual application.

[0039] like Figure 7-10 As shown, optionally, based on the above technical solution, multiple sawtooth structures A are connected end-to-end sequentially on the boundary. Specifically, each sawtooth structure A includes two intersecting sides, with the intersection point as the vertex and the non-intersecting points as the endpoints. Multiple sawtooth structures A can be connected end-to-end sequentially through the endpoints, so that multiple continuous sawtooth structures A are formed on the side surface of the piezoelectric layer, or on the side surface of the upper electrode, piezoelectric layer, and lower electrode. The corresponding vertical projection boundary also includes multiple sawtooth structures A connected end-to-end sequentially.

[0040] Figure 11 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention. Figure 11 As shown, optionally, based on the above technical solution, multiple sawtooth structures A with a set distance can also be provided on the side of the piezoelectric layer, or on the side of the upper electrode, piezoelectric layer and lower electrode, and multiple discontinuous sawtooth structures A can be formed on the boundary of the corresponding vertical projection.

[0041] like Figure 7-11 As shown, optionally, based on the above technical solution, multiple sawtooth structures A have the same shape. This arrangement can reduce the manufacturing difficulty and cost of the sawtooth structures.

[0042] Figure 12 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention. Figure 12As shown, optionally, based on the above technical solution, the shapes of the multiple sawtooth structures can also be different. Specifically, multiple sawtooth structures of the same shape can be provided on the side of the piezoelectric layer, or on the side of the upper electrode, piezoelectric layer and lower electrode, or multiple sawtooth structures of different shapes can be provided. The sawtooth structure can be specifically set according to the actual application and the effect of the sawtooth structure in preventing the generation of standing waves other than longitudinal bulk acoustic waves.

[0043] Furthermore, the dimensions of multiple sawtooth structures can be the same or different, and can be set according to needs.

[0044] Optionally, based on the above technical solution, the shape of the sawtooth structure includes a triangle or a trapezoid. This design simplifies the manufacturing process of the sawtooth structure and reduces manufacturing costs. Figure 13 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention. Figure 2-3 , Figure 5 ,as well as Figure 7-12 This illustrates the case where the sawtooth structure is triangular. Figure 13 The diagram shows the case where the sawtooth structure A' is trapezoidal. The specific shape of the sawtooth structure can be selected based on the actual application and the effect of the sawtooth structure in preventing the generation of other forms of standing waves besides longitudinal volume acoustic waves.

[0045] refer to Figure 11 Optionally, based on the above technical solution, the center-to-center distance B between adjacent sawtooth structures A is greater than or equal to 2 micrometers. This setting further reduces the manufacturing difficulty of the sawtooth structure A and lowers the manufacturing cost.

[0046] Figure 14 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention; Figure 15 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention. Figure 3 This illustrates a piezoelectric layer with multiple sequentially connected sawtooth structures A of identical size on each side along its thickness direction, where the center-to-center distance B between adjacent sawtooth structures A is a standard dimension. Figure 14-15 The diagram shows that the piezoelectric layer has multiple sequentially connected sawtooth structures A of the same size on each side along the thickness direction, with the center spacing B between adjacent sawtooth structures A being sparse and dense, respectively. Figure 16 This is a schematic diagram showing the impedance and frequency function curves of another bulk acoustic resonator provided in an embodiment of the present invention. Curve G is... Figure 3 The corresponding function curves of impedance and frequency for the bulk acoustic resonator, curves E and F are respectively Figure 14 and Figure 15 The corresponding function curve of the bulk acoustic resonator's impedance versus frequency. For example... Figure 16As shown, the smoothness of curves E, G, and F increases sequentially, and the center-to-center spacing B of adjacent sawtooth structures A in each corresponding bulk acoustic wave resonator decreases sequentially. Therefore, the smaller the center-to-center spacing B, the smoother the impedance-frequency function curve of the bulk acoustic wave resonator, the less noise the resonator has, and the better its performance. Thus, it is preferable to make the multiple sawtooth structures A on the side of the piezoelectric layer, or on the side of the upper electrode, piezoelectric layer, and lower electrode, as denser as possible to better prevent other forms of standing waves. For example, the center-to-center spacing B of adjacent sawtooth structures A can be set to a denser size, ranging from 2µm to 5µm; a normal size, ranging from 5µm to 10µm; or a sparse size, ranging from 10µm to 20µm.

[0047] Figure 17 This is a vertical projection schematic diagram of another bulk acoustic resonator provided in an embodiment of the present invention; Figure 18 This is a schematic diagram of the vertical projection of another bulk acoustic wave resonator provided in an embodiment of the present invention. Optionally, based on the above technical solution, the shape of the vertical projection of the bulk acoustic wave resonator on a plane perpendicular to its thickness direction includes a polygon. Specifically, the shape of the vertical projection of the bulk acoustic wave resonator on a plane perpendicular to its thickness direction refers to the approximate shape of the outline of the vertical projection. The polygon can be a planar figure composed of three or more line segments connected end to end in sequence, including triangles, quadrilaterals, and pentagons, etc. It can be a regular polygon or an irregular polygon, wherein the quadrilateral can be a square or a rectangle. Figure 3 and Figure 7-15 The diagram illustrates the arrangement of the sawtooth structure on a bulk acoustic resonator when its outer contour, projected vertically onto a plane perpendicular to its thickness direction, is square. Figure 17-18 The diagrams illustrate the arrangement of sawtooth structures on bulk acoustic resonators when the outer contour of the resonator's vertical projection onto a plane perpendicular to its thickness direction is triangular and quadrilateral, respectively. Bulk acoustic resonators can have different shapes depending on their specific structure and application, and sawtooth structures can be incorporated into bulk acoustic resonators of different shapes according to any embodiment of this invention.

[0048] Optionally, based on the above technical solution, the upper and lower electrodes can be made of any one of gold, molybdenum, aluminum, chromium, and nickel, or other materials used to manufacture the upper and lower electrodes. The piezoelectric layer can be made of any one of lead zirconate titanate piezoelectric ceramic, zinc oxide, and aluminum nitride. Specifically, any of the above materials can be selected based on the structure and application scenario of the bulk acoustic wave resonator, as well as the conductivity requirements of the upper electrode, lower electrode, and piezoelectric layer.

[0049] Note that the above are only preferred embodiments of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments, and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments and may include many other equivalent embodiments without departing from the concept of the present invention. The scope of the present invention is determined by the scope of the appended claims.

Claims

1. A bulk acoustic resonator suitable for integrated circuits, characterized in that, include: An upper electrode, a piezoelectric layer, and a lower electrode, wherein the piezoelectric layer is disposed between the upper electrode and the lower electrode; The piezoelectric layer includes at least a portion of the boundary of the vertical projection of the lower electrode, comprising a plurality of sawtooth structures; when the transverse bulk acoustic wave generated by the piezoelectric layer after being energized propagates to the surface of the piezoelectric layer in contact with air, diffuse reflection will occur; The sides of the upper electrode, the piezoelectric layer, and the lower electrode are all provided with multiple sawtooth structures, and at least a portion of the boundaries of the upper electrode and the lower electrode on the plane perpendicular to the thickness direction of the bulk acoustic resonator include multiple sawtooth structures.

2. The bulk acoustic resonator according to claim 1, characterized in that, The center-to-center distance between adjacent sawtooth structures is greater than or equal to 2 micrometers.

3. The bulk acoustic resonator according to claim 1, characterized in that, All boundaries of the piezoelectric layer in the vertical projection of the lower electrode include multiple serrated structures.

4. The bulk acoustic resonator according to claim 3, characterized in that, Multiple of the aforementioned sawtooth structures are connected end to end on the boundary.

5. The bulk acoustic resonator according to claim 1, characterized in that, The serrated structure can be triangular or trapezoidal in shape.

6. The bulk acoustic resonator according to claim 1, characterized in that, The shape of the bulk acoustic resonator's vertical projection onto a plane perpendicular to its thickness direction includes a polygon.

7. The bulk acoustic resonator according to claim 1, characterized in that, The upper electrode and the lower electrode are made of any one of gold, molybdenum, aluminum, chromium and nickel.

8. The bulk acoustic resonator according to claim 1, characterized in that, The piezoelectric layer is made of any one of lead zirconate titanate piezoelectric ceramic, zinc oxide, and aluminum nitride.

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