Bulk acoustic wave resonator

Abstract

The invention discloses a bulk acoustic wave resonator. The bulk acoustic wave resonator comprises a substrate and a first electrode layer arranged on one side of the substrate, wherein a cavity is formed between the first electrode layer and the substrate; the piezoelectric layer is arranged on one side, far away from the substrate, of the first electrode layer; the second electrode layer is arranged on one side, far away from the first electrode layer, of the piezoelectric layer; the shape of at least one of the first electrode layer and the second electrode layer is a fixed-width curve; wherein the projection of one electrode layer in the shape of a fixed-width curve on the piezoelectric layer falls within the projection of the other electrode layer on the piezoelectric layer, and the active excitation part of the resonator is determined by the overlapped part of the first electrode and the second electrode, namely the area of the fixed-width curve. According to the embodiment of the invention, the opportunity that transverse waves resonate when sound waves are propagated in the piezoelectric material can be reduced, so that the noise generated when the bulk acoustic wave resonator works is reduced.

Description

Technical Field

[0001] This invention relates to the field of radio frequency technology, and in particular to a bulk acoustic resonator. Background Technology

[0002] A film bulk acoustic resonator (FBAR) is a miniature device that operates using the piezoelectric effect and is widely used in wireless communication, sensors, and filters. FBARs are characterized by their small size, low power consumption, and high performance, making them suitable for integrated circuit design.

[0003] In existing technologies, bulk acoustic wave resonators consist of an upper electrode, a piezoelectric layer, and a lower electrode. In practical applications, bulk acoustic wave resonators primarily excite longitudinal modes in the thickness direction, and these longitudinal modes are a key parameter affecting the resonator's performance. However, in addition to the desired longitudinal modes, transverse modes can also be unexpectedly generated in bulk acoustic wave resonators, leading to an increase in additional noise. Summary of the Invention

[0004] This invention provides a bulk acoustic resonator to reduce transverse waves generated during operation and reduce additional noise.

[0005] According to one aspect of the present invention, a bulk acoustic resonator is provided, comprising: a substrate and a first electrode layer disposed on one side of the substrate, wherein a cavity is formed between the first electrode layer and the substrate;

[0006] A piezoelectric layer is disposed on the side of the first electrode layer away from the substrate;

[0007] A second electrode layer is disposed on the piezoelectric layer on a side away from the first electrode layer;

[0008] In the first electrode layer and the second electrode layer, at least one has a shape of a fixed-width curve; wherein the projection of the electrode layer with the shape of the fixed-width curve onto the piezoelectric layer falls within the projection of the other electrode layer onto the piezoelectric layer, and wherein the active excitation portion of the resonator is determined by the overlapping portion of the first electrode and the second electrode, i.e., the region of the fixed-width curve.

[0009] Optionally, in the first electrode layer and the second electrode layer, at least one has a Reilly polygon shape.

[0010] Optionally, in the first electrode layer and the second electrode layer, at least one of them is in the shape of a Reich triangle or a Reich pentagon.

[0011] Optionally, in the first electrode layer and the second electrode layer, at least one of them has a shape that is a fixed-width curve with an extended regular polygonal side length.

[0012] Optionally, corrosion holes are provided at the vertices of the regular polygon along the fixed-width curve extending the side length of the regular polygon.

[0013] Optionally, in the first electrode layer and the second electrode layer, at least one of them is a fixed-width curve that extends the side length of an equilateral triangle or a fixed-width curve that extends the side length of a regular pentagon.

[0014] Optionally, an corrosion hole is provided at each vertex of the equilateral triangle in the fixed-width curve extending the side length of the equilateral triangle.

[0015] Optionally, an corrosion hole is provided at each vertex of the regular pentagon along the fixed-width curve that extends the side length of the regular pentagon.

[0016] The technical solution of this invention, by setting the shape of at least one of the first electrode layer or the second electrode layer to a fixed-width curve shape, so that the electrode layer has only one characteristic dimension in the lateral direction, can reduce the chance of lateral wave resonance during the propagation of sound waves in the piezoelectric material, thereby reducing the noise when the bulk acoustic resonator is working.

[0017] It should be understood that the description in this section is not intended to identify key or essential features of the embodiments of the present invention, nor is it intended to limit the scope of the invention. Other features of the invention will become readily apparent from the following description. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the structure of a bulk acoustic resonator provided in an embodiment of the present invention;

[0020] Figure 2 A schematic diagram of a Reichstag triangle provided in an embodiment of the present invention;

[0021] Figure 3 A schematic diagram of a Reich pentagon provided for an embodiment of the present invention;

[0022] Figure 4 A schematic diagram of a fixed-width curve for extending the side length of a triangle, provided as an embodiment of the present invention;

[0023] Figure 5 A schematic diagram of a fixed-width curve for extending the side length of a pentagon, provided as an embodiment of the present invention;

[0024] Figure 6 The figure shows the test results of the impedance spectrum of a Reilly pentagonal oscillator and a circular oscillator provided in the embodiments of the present invention. Detailed Implementation

[0025] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0026] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this invention are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of the invention described herein can be implemented in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover a non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0027] Figure 1 This is a schematic diagram of a bulk acoustic resonator provided in an embodiment of the present invention. This embodiment is applicable to high-frequency signal processing applications such as wireless communication, filters, and sensors. Figure 1 As shown, the bulk acoustic wave resonator includes: a substrate 110 and a first electrode layer 120 disposed on one side of the substrate 110, with a cavity 111 between the first electrode layer 120 and the substrate 110; a piezoelectric layer 130 disposed on the side of the first electrode layer 120 away from the substrate 110; and a second electrode layer 140 disposed on the side of the piezoelectric layer 130 away from the first electrode layer 120. At least one of the first electrode layer 120 and the second electrode layer 140 has a shape of a constant-width curve. The projection of the electrode layer with the shape of a constant-width curve onto the piezoelectric layer 130 falls within the projection of the other electrode layer onto the piezoelectric layer 130. The active excitation portion of the resonator is determined by the overlapping portion of the first electrode layer 120 and the second electrode layer 140, i.e., the region of the constant-width curve.

[0028] Specifically, substrate 110 refers to the base material of the bulk acoustic wave resonator, used to provide physical support and mechanical stability. Commonly used substrate 110 materials include silicon (Si), sapphire (Al₂O₃), and quartz. First electrode layer 120 refers to the electrode in contact with substrate 110. First electrode layer 120 is generally made of metallic materials, such as aluminum (Al), molybdenum (Mo), or titanium (Ti). Cavity 111 refers to the spatial region between first electrode layer 120 and substrate 110. Piezoelectric layer 130 refers to the core part of the bulk acoustic wave resonator. Commonly used piezoelectric materials include aluminum nitride (AlN), lithium niobate (LiNbO₃), lead bismuth titanate (PZT), and lead zirconate titanate (PZT). The second electrode layer 140 is located on the side of the piezoelectric layer 130 away from the substrate 110. The second electrode layer 140 is typically made of the same or similar metallic material as the first electrode layer 120, such as aluminum (Al) or molybdenum (Mo), to maintain good conductivity and similar thermal expansion characteristics. The first electrode layer 120, the piezoelectric layer 130, and the second electrode layer 140 constitute the oscillator of a resonator. Applying an electric field to the piezoelectric layer 130 by the first electrode layer 120 and the second electrode layer 140 can induce mechanical deformation, thereby exciting sound waves. In this embodiment of the invention, the design of the cavity 111 can confine the sound waves excited by the electric field within the piezoelectric layer 130 and the two electrode layers, thereby reducing energy loss and improving the performance of the bulk acoustic resonator.

[0029] A curve with constant width is defined as follows: If a plane contains several intersecting straight lines that form a closed polygon, take a fixed-length line segment on one of the straight lines passing through that vertex (denoted as the first line) and draw an arc outwards from the polygon, so that the endpoint of the arc drawn from the two endpoints of the line segment falls exactly on another straight line passing through that vertex (denoted as the second line). Then, taking the second vertex of the polygon where the second and third lines intersect as the center, draw arcs with the same length of line segment as the radius, smoothly connecting with the first two arcs, with the endpoint falling on the third line. Continue in this manner, drawing arcs with subsequent vertices of the polygon as centers and fixed-length line segments as radii, until finally returning to the starting point, forming a closed curve. This curve is called a curve with constant width. Every curve with constant width has a fixed width, or diameter. Circles and Reichstag polygons are special cases of curves with constant width. Curves with the same width have the same perimeter.

[0030] In this embodiment of the invention, at least one electrode layer adopts a constant-width curve shape, with only one characteristic dimension in the transverse direction of the resonator, namely the width of the constant-width curve. This reduces the generation of transverse resonant waves and ensures that the sound waves propagate in the piezoelectric material in the expected longitudinal wave manner. Furthermore, the constant-width curve can smooth the edges of the electrodes, reducing the interference of edge effects on sound wave propagation, thereby reducing the excitation of unnecessary transverse waves.

[0031] The technical solution of this invention, by setting the shape of at least one of the first electrode layer or the second electrode layer to a fixed-width curve shape, so that the electrode layer has only one characteristic dimension in the lateral direction, can reduce the chance of lateral wave resonance during the propagation of sound waves in the piezoelectric material, thereby reducing the noise when the bulk acoustic resonator is working.

[0032] Based on the above embodiments, optionally, at least one of the first electrode layer 120 and the second electrode layer 140 has a Reichstag polygon shape.

[0033] Specifically, a Reilly polygon refers to a polygon with a fixed width. The width of the Reilly polygon remains constant in any direction, thus exhibiting only one characteristic dimension in the transverse direction, and generating transverse resonance only at a specific resonant frequency. Furthermore, the propagation path of the transverse wave passes through the vertices of the Reilly polygon; therefore, setting etched holes at the vertices of the Reilly polygon can scatter the transverse wave, thereby suppressing transverse wave resonance. These etched holes are through-holes penetrating the first electrode layer 120, the second electrode layer 140, and the piezoelectric layer 130.

[0034] In this embodiment of the invention, by adding through-holes penetrating the two electrode layers and the piezoelectric layer 130 at the vertices of the Reilly polygon, the propagation path of the transverse wave can be altered, thereby eliminating the resonance of the transverse wave. Therefore, the boundary design of the Reilly polygon combined with the through-holes at the vertices can effectively control the transmission and resonance of the transverse wave and reduce its intensity.

[0035] The technical solution of this invention, by setting the shape of at least one of the first electrode layer and the second electrode layer to a Reylow polygon, can effectively reduce the transmission and resonance of transverse waves in the bulk acoustic resonator, thereby reducing noise.

[0036] Based on the above embodiments, optionally, in the first electrode layer 120 and the second electrode layer 140, at least one of them has a Reilly triangle or a Reilly pentagon shape.

[0037] Specifically, Figure 2 This is a schematic diagram of a Reichstag triangle provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of a Reichstag pentagon provided as an embodiment of the present invention. Figure 2As shown, in an equilateral triangle ABC with side length d, arcs are drawn with vertex A as the center and side length d as the radius, connecting vertices B and C; arcs are drawn with vertex B as the center and side length d as the radius, connecting vertices A and C; and arcs are drawn with vertex C as the center and side length d as the radius, connecting vertices A and B. The shape formed by these three arcs is the Reilly triangle. The width of the Reilly triangle in each direction is equal to the side length d of the equilateral triangle ABC, meaning the diameter of the Reilly triangle is d. The perimeter of the Reilly triangle is equal to the perimeter of a circle with diameter d. Since curves of the same width have the same perimeter, the lateral energy exchange rate of a circular oscillator and a Reilly triangle oscillator of the same width is the same; for the same area, the circle has the smallest perimeter and the smallest energy exchange. Furthermore, the Reilly triangle is the smallest shape that can be formed by curves of the same width.

[0038] A constant-width curve has a fixed diameter in the transverse direction, which is its maximum width. Whether an oscillator induces transverse vibration depends on the thickness and transverse dimensions of the oscillator, while whether the induced Rayleigh-Lamb wave transverse vibration forms a standing wave is determined by the wavelength of the transverse vibration and the diameter of the constant-width oscillator. For a Reilly triangle oscillator, although its shape differs from that of a circular oscillator, its transverse vibration characteristics are the same as those of a circular oscillator. As long as the diameter of the Reilly triangle is not set to meet the conditions for the formation of a standing wave from the transverse wave, the noise caused by the transverse wave can be reduced or eliminated.

[0039] In some embodiments, such as Figure 3 As shown, on the regular pentagon EFGHI, with vertex E as the center and the length e of the diagonal from vertex E to vertex G as the radius, an arc is drawn connecting vertices G and H; with vertex F as the center and the length e of the diagonal from vertex E to vertex G as the radius, an arc is drawn connecting vertices I and H; with vertex G as the center and the length e of the diagonal from vertex E to vertex G as the radius, an arc is drawn connecting vertices I and E; with vertex H as the center and the length e of the diagonal from vertex E to vertex G as the radius, an arc is drawn connecting vertices E and F; with vertex I as the center and the length e of the diagonal from vertex I to vertex G as the radius, an arc is drawn connecting vertices G and F. The figure formed by these five arcs is a Reilow pentagon. The width of the Reilow pentagon in each direction is equal to the length e of the diagonal of the regular pentagon EFGHI, that is, the diameter of the Reilow pentagon is e.

[0040] In this embodiment of the invention, the electrode layer formed by the Reilly triangle or Reilly pentagon has only one characteristic dimension in the lateral direction, namely its diameter. As long as its diameter does not meet the conditions for the formation of a standing wave in the transverse direction, the generation of the transverse standing wave can be suppressed, reducing additional noise. Therefore, corrosion holes can be set at the vertices of the Reilly triangle or Reilly pentagon.

[0041] Based on the above embodiments, optionally, in the first electrode layer 120 and the second electrode layer 140, at least one of them has a shape that is a fixed-width curve with an extended regular polygonal side length.

[0042] Specifically, the side length of the regular polygon is an odd number greater than or equal to 3. The fixed-width curve for extending the side length of the regular polygon is obtained as follows: Extend the regular polygon by an appropriate length in both directions along its diagonal. Then, using each vertex of the regular polygon as its center, draw the first arc with the length of the extension connecting to that vertex as its radius. This first arc connects to the endpoint of the adjacent extension. Next, using the sum of the diagonal and the length of the extension as its radius, draw the second arc along the diagonal. This second arc connects to the other endpoint of the adjacent extension. Finally, the closed curve formed by each arc is the fixed-width curve for extending the side length of the regular polygon. The fixed-width curve for extending the side length of the regular polygon has the same width in every direction, i.e., its diameter.

[0043] Based on the above embodiments, optionally, corrosion holes can be provided at the vertices of the regular polygon with a fixed width curve that extends the side length of the regular polygon.

[0044] Specifically, corrosion holes refer to small holes that penetrate the sandwich structure formed by the first electrode layer 120, the piezoelectric layer 130, and the second electrode layer 140. In the design of bulk acoustic wave vibrators or resonators, corrosion holes can be used to corrode the sacrificial layer in the cavity 111 or to release the pressure inside the cavity 111.

[0045] In this embodiment of the invention, the combination of etched holes at the vertices of the polygon and a fixed-width curve extending the side length of the regular polygon can suppress the formation of clutter in the bulk acoustic resonator and achieve a higher quality factor. The combination of etched holes and a fixed-width curve extending the side length of the regular polygon can also prevent the formation of transverse standing waves, thereby suppressing resonator clutter. Furthermore, after etched holes are provided at the vertices of the polygon in the resonator with the fixed-width curve shape, there is no need to reserve etched through-holes on the outside of the resonator, which can reduce the area of ​​the resonator and thus lower costs.

[0046] Based on the above embodiments, optionally, in the first electrode layer 120 and the second electrode layer 140, at least one of them is a fixed-width curve with an extended side length of an equilateral triangle or a fixed-width curve with an extended side length of a regular pentagon.

[0047] Specifically, Figure 4 This is a schematic diagram of a fixed-width curve for extending the side length of a triangle, provided as an embodiment of the present invention. Figure 5 This is a schematic diagram of a fixed-width curve for extending the side length of a pentagon, provided as an embodiment of the present invention. (See diagram below.) Figure 4As shown, extend the diagonal of a triangle with side length d by a length e to both ends. Using vertex A as the center and the length e of the extended line as the radius, draw an arc along the direction of the extended line connecting to vertex A, connecting to the endpoint of the adjacent extended line. Then, using vertex A as the center and the sum of the length d of the triangle's diagonal and the length e of its extended line as the radius, draw another arc along the direction of the diagonal connecting to vertex A, connecting to the endpoint of the adjacent extended line. Similarly, using vertex B as the center and the sum of the length e of the extended line as the radius, draw an arc along the direction of the extended line connecting to vertex B, connecting to the endpoint of the adjacent extended line. Finally, using vertex B as the center and the sum of the length d of the triangle's diagonal and the length e of its extended line as the radius, draw another arc along the direction of the diagonal connecting to vertex B, connecting to the endpoint of the adjacent extended line. Using vertex C as the center and the length *e* of its extension as the radius, draw an arc along the extension of the line connecting to vertex C, connecting the endpoints of the adjacent extensions. Then, using vertex C as the center and the length *d* of the triangle's diagonal plus the length *e* of its extension as the radius, draw another arc along the diagonal connecting to vertex C, connecting the endpoints of the adjacent extensions. The closed curve formed by these six arcs is a fixed-width curve extending the side length of the triangle. (Example:) Figure 5 As shown, similar to the steps above for obtaining a fixed-width curve for extending the side length of a triangle, a fixed-width curve for extending the side length of a pentagon can be obtained.

[0048] Based on the above embodiments, optionally, an corrosion hole can be provided at each vertex of the equilateral triangle of the fixed-width curve with extended triangle side length.

[0049] In this embodiment of the invention, the constant-width curve extending the side length of the equilateral triangle has only one characteristic dimension in the transverse direction, namely its diameter, thus generating transverse resonance only at a specific resonant frequency. Moreover, the propagation path of the transverse wave passes through the vertex of the equilateral triangle, and setting corrosion holes at the vertex can scatter the propagation of the transverse wave, thereby suppressing the generation of transverse standing waves and effectively reducing unnecessary noise generated during the operation of the bulk acoustic resonator.

[0050] Based on the above embodiments, optionally, an corrosion hole can be provided at the position of each vertex of the regular pentagon in the fixed-width curve that extends the side length of the regular pentagon.

[0051] In this embodiment of the invention, setting corrosion holes at the vertices of the regular pentagon can scatter the propagation of transverse waves, thereby suppressing the generation of transverse standing waves and effectively reducing unnecessary noise generated during the operation of the bulk acoustic resonator.

[0052] Based on the above embodiments, experiments were conducted on a circular oscillator and a Reylow pentagon, and the results are as follows:

[0053] Leroy pentagon round Zp 1858 1342 Zs 1.26 1.23 Zp / Zs 1480 1091

[0054] Where Zp is the parallel resonant impedance of the resonator, Zs is the series resonant impedance of the resonator, and Zp / Zs is the quality factor. Figure 6 The image shows the test results of the impedance spectra of a Reylow pentagonal oscillator and a circular oscillator provided in an embodiment of the present invention. Figure 6 As shown, the blue curve represents the impedance spectrum of the Reich pentagonal oscillator, and the red curve represents the impedance spectrum of the circular oscillator. The horizontal axis represents frequency in GHz, and the vertical axis represents impedance, with the maximum impedance being Zp and the minimum impedance being Zs. (Reference) Figure 6 As can be seen from the above experimental results, the quality factor of a Reilly pentagonal oscillator with the same area is higher than that of a circular oscillator.

[0055] It should be understood that the various forms of processes shown above can be used, with steps reordered, added, or deleted. For example, the steps described in this invention can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution of this invention can be achieved, and this is not limited herein.

[0056] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A bulk acoustic resonator, characterized in that, include: A substrate and a first electrode layer disposed on one side of the substrate, wherein there is a cavity between the first electrode layer and the substrate; A piezoelectric layer is disposed on the side of the first electrode layer away from the substrate; A second electrode layer is disposed on the piezoelectric layer on a side away from the first electrode layer; In the first electrode layer and the second electrode layer, at least one has a shape that is a constant-width curve; wherein the projection of the electrode layer with the shape of the constant-width curve onto the piezoelectric layer falls within the projection of the other electrode layer onto the piezoelectric layer.

2. The bulk acoustic resonator according to claim 1, characterized in that, In the first electrode layer and the second electrode layer, at least one has a Reilly polygon shape.

3. The bulk acoustic resonator according to claim 2, characterized in that, In the first electrode layer and the second electrode layer, at least one has a Reichstag triangle or a Reichstag pentagon shape.

4. The bulk acoustic resonator according to claim 1, characterized in that, In the first electrode layer and the second electrode layer, at least one has a shape that is a fixed-width curve with an extended regular polygonal side length.

5. The bulk acoustic resonator according to claim 4, characterized in that, Etching holes are provided at the vertices of the regular polygon along the fixed-width curve of the extended regular polygon side length.

6. The bulk acoustic resonator according to claim 5, characterized in that, In the first electrode layer and the second electrode layer, at least one has a shape that is a fixed-width curve extending the side length of an equilateral triangle or a fixed-width curve extending the side length of a regular pentagon.

7. The bulk acoustic resonator according to claim 6, characterized in that, An corrosion hole is provided at each vertex of the equilateral triangle in the fixed-width curve extending the side length of the equilateral triangle.

8. The bulk acoustic resonator according to claim 6, characterized in that, An corrosion hole is provided at each vertex of the regular pentagon along the fixed-width curve extending the side length of the regular pentagon.

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