Acoustic filter and method of making the same

Abstract

The application relates to the field of wireless communication technology and provides an acoustic filter and a preparation method thereof.The preparation method comprises the following steps: S1, providing a substrate, forming an acoustic layer on the surface of the substrate, and forming an effective acoustic structure by using the acoustic layer; wherein the effective acoustic structure comprises an acoustic resonance structure, an input end part, an output end part and a ring-shaped grounding end; S2, forming a separation layer on the side of the effective acoustic structure away from the substrate, so that the separation layer completely covers the acoustic structure, and etching an electrical connection window through the separation layer; S3, forming a connecting layer on the side of the separation layer away from the effective acoustic structure, so that the connecting layer completely covers the separation layer, and the connecting layer is connected with the ring-shaped grounding end of the acoustic layer after penetrating through the electrical connection window, thereby obtaining the acoustic filter; wherein the thickness of the connecting layer is the same as the thickness of the acoustic layer.The acoustic filter has low manufacturing cost and is miniaturized as a whole.

Description

Technical Field

[0001] This invention relates to the field of wireless communication technology, and in particular to an acoustic filter and its fabrication method. Background Technology

[0002] With the full commercialization of 5G mobile communication technology and the explosive growth of IoT devices, modern wireless communication systems are rapidly evolving towards higher frequencies, greater integration, and multi-mode operation. As a key frequency control component in the RF front-end module, surface acoustic wave (SAW) filters play an irreplaceable role in signal selection and interference suppression. However, the physical size of traditional SAW filters has become one of the main bottlenecks restricting further miniaturization and performance improvement of the entire RF module.

[0003] This challenge stems primarily from two fundamental driving forces. First, there is the rigid constraint of "limited space." Space is extremely limited within smartphones and other terminal devices. To support multiple frequency bands (such as the n77, n78, and n79 bands of 5G Sub-6GHz), dozens or even hundreds of filters must be integrated onto a single motherboard, forming complex filter banks. The size of traditional surface acoustic wave (SAW) filters is no longer sufficient to meet the demands of high-density integration, forcing the industry to shift towards smaller package solutions. Second, there is the inherent requirement for "system performance." The size of a filter is directly related to the acoustic wavelength of its resonator. Reducing the size can lead to a decrease in the quality factor (Q value), an increase in insertion loss, and a narrowing of bandwidth, which contradicts the system's requirements for high selectivity and low loss.

[0004] In related technologies, the core technical path to achieve size reduction has long focused on improving the operating frequency and energy confinement capability of devices. Traditional methods include using piezoelectric substrate materials with higher sound velocity (such as higher-order cut lithium tantalate and lithium niobate) or reducing the electrode linewidth of interdigital transducers. However, these approaches all encounter significant bottlenecks: high-velocity materials are often accompanied by a decrease in electromechanical coupling coefficient, resulting in bandwidth limitation; and when the electrode linewidth enters the submicron level, it not only faces the limits of traditional photolithography processes but also causes a sharp increase in electrode resistance, resulting in deterioration of insertion loss and a decrease in power tolerance. In addition, conventional SAW energy is concentrated on the surface, limiting its performance at higher frequencies and making it difficult to achieve high-performance resonance in a smaller area.

[0005] Therefore, the industry continues to explore breakthrough technologies, such as novel structures like Incredible High Performance Surface Acoustic Wave (IHP-SAW) and Laterally Excited Bulk Acoustic Resonator (XBAR) based on thin-film substrates. These structures achieve excellent performance at higher frequencies by exciting and confining acoustic wave energy within multilayer thin films. The development of these technologies signifies that the miniaturization of surface acoustic wave filters has moved beyond simple geometric scaling to a deeper innovation stage based on the collaborative design of new material systems, new acoustic modes, and three-dimensional micro / nano structures. Against this backdrop, how to break through size limits while comprehensively optimizing core performance indicators such as insertion loss, bandwidth, out-of-band rejection, and power capacity has become the focus of current technology research and patent strategy.

[0006] However, with limited chip area, conventional surface acoustic wave (SAW) filters often use bridging structures to achieve multi-layer metal traces and interconnections. This structure increases the layout size of SAW devices that require multi-layer metal traces, which increases material costs and occupies the effective chip area of ​​acoustic devices, thus affecting the improvement of filter performance. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the present invention proposes a method for manufacturing an acoustic filter to solve the problems of high manufacturing cost, large overall area and poor performance of existing acoustic filters.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] In a first aspect, embodiments of the present invention provide a method for fabricating an acoustic filter, the method comprising the following steps:

[0010] S1. A substrate is provided, an acoustic layer is formed on the surface of the substrate, and an effective acoustic structure is formed using the acoustic layer; wherein, the effective acoustic structure includes an acoustic resonant structure, an input end, an output end, and a ring-shaped grounding end, the input end and the output end are respectively connected to opposite ends of the acoustic resonant structure, and the ring-shaped grounding end is arranged around the acoustic resonant structure;

[0011] S2. A separation layer is formed on the side of the effective acoustic structure away from the substrate, such that the separation layer completely covers the effective acoustic structure, and an electrical connection window is etched through the separation layer; wherein the thickness of the separation layer is 5~25nm;

[0012] S3. A connecting layer is formed on the side of the separation layer away from the effective acoustic structure, so that the connecting layer completely covers the separation layer, and the connecting layer passes through the electrical connection window and is connected to the ring-shaped ground terminal of the acoustic layer to obtain an acoustic filter; wherein, the thickness of the connecting layer is the same as the thickness of the acoustic layer.

[0013] Preferably, in step S1, the acoustic layer is made of aluminum or a copper-aluminum alloy.

[0014] Preferably, the effective acoustic structure is fabricated using a metal deposition and patterning process.

[0015] Preferably, in step S2, the etching process of the electrical connection window is carried out by dry etching or wet etching.

[0016] Preferably, the thickness of the separation layer is 20 nm.

[0017] Preferably, in step S2, the separation layer is formed by chemical vapor deposition or physical vapor deposition.

[0018] Preferably, in step S3, the connecting layer and the annular grounding terminal are connected by direct metal contact.

[0019] Preferably, the graphical structure of the connection layer corresponds to the position of the electrical connection window.

[0020] Preferably, the substrate is made of a piezoelectric material.

[0021] Secondly, embodiments of the present invention provide an acoustic filter, which is prepared by the above-described method for preparing an acoustic filter.

[0022] Compared with related technologies, in the embodiments of the present invention, an acoustic layer is formed on the surface of a substrate, and an effective acoustic structure is formed using the acoustic layer. The effective acoustic structure includes an acoustic resonant structure, an input end, an output end, and a ring-shaped grounding end. The input end and the output end are respectively connected to the opposite ends of the acoustic resonant structure, and the ring-shaped grounding end is arranged around the acoustic resonant structure. A separation layer is formed on the side of the effective acoustic structure away from the substrate, so that the separation layer completely covers the effective acoustic structure, and an electrical connection window is etched through the separation layer. A connection layer is formed on the side of the separation layer away from the effective acoustic structure, so that the connection layer completely covers the separation layer, and the connection layer passes through the electrical connection window and connects to the ring-shaped grounding end of the acoustic layer, thus obtaining an acoustic filter. In this way, by separating the input signal, output signal, and ring-shaped grounding end of the complex acoustic device through a thin passivation layer separation layer, the device area is significantly reduced without affecting the performance of the surface acoustic wave filter, realizing the miniaturization of the filter device and further improving the overall performance of the filter device. Attached Figure Description

[0023] The present invention will now be described in detail with reference to the accompanying drawings. The above and other aspects of the present invention will become clearer and more readily understood through the detailed description following the accompanying drawings. In the drawings:

[0024] Figure 1 A flowchart illustrating the fabrication method of an acoustic filter provided in an embodiment of the present invention;

[0025] Figure 2 This is a top view of the corresponding structure obtained after step S1 in the method for preparing an acoustic filter according to an embodiment of the present invention.

[0026] Figure 3 This is a top view of the corresponding structure obtained after step S2 in the method for preparing an acoustic filter according to an embodiment of the present invention.

[0027] Figure 4 This is a top view of the corresponding structure obtained after step S3 in the method for preparing an acoustic filter according to an embodiment of the present invention.

[0028] Figure 5 A schematic diagram of the structure corresponding to step S1 of the acoustic filter fabrication method provided in the embodiment of the present invention;

[0029] Figure 6 A schematic diagram of the separation layer corresponding to step S2 of the acoustic filter fabrication method provided in this embodiment of the invention;

[0030] Figure 7 A schematic diagram of the electrical connection window corresponding to step S2 of the acoustic filter fabrication method provided in this embodiment of the invention;

[0031] Figure 8 This is a schematic diagram of the structure corresponding to step S3 of the acoustic filter fabrication method provided in the embodiment of the present invention.

[0032] Among them, 100 is the acoustic filter, 1 is the substrate, 2 is the acoustic layer, 21 is the acoustic resonant structure, 22 is the input end, 23 is the output end, 24 is the ring ground end, 3 is the separation layer, 31 is the electrical connection window, and 4 is the connection layer. Detailed Implementation

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein in the specification of the application is for the purpose of describing particular embodiments only and is not intended to be limiting of the application; the terms "comprising" and "having," and any variations thereof, in the specification, claims, and foregoing drawings of this application, are intended to cover non-exclusive inclusion. The terms "first," "second," etc., in the specification, claims, or foregoing drawings of this application are used to distinguish different objects, not to describe a particular order.

[0034] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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 are within the scope of protection of the present invention.

[0036] Example 1

[0037] Please see Figures 1-8 As shown, this embodiment of the invention provides a method for fabricating an acoustic filter, the method comprising the following steps:

[0038] S1. A substrate 1 is provided, and an acoustic layer 2 is formed on the surface of the substrate 1, and an effective acoustic structure is formed using the acoustic layer 2. The effective acoustic structure includes an acoustic resonant structure 21, an input end 22, an output end 23, and a ring-shaped grounding end 24. The input end 22 and the output end 23 are respectively connected to opposite ends of the acoustic resonant structure 21, and the ring-shaped grounding end 24 is arranged around the acoustic resonant structure 21. Specifically, the substrate 1 is generally rectangular, used to provide support for the acoustic layer 2, and the input end 22 and the output end 23 are located on opposite sides of the long side of the substrate 1. The input end of the acoustic resonant structure 21 is connected to the input end 22, the output end of the acoustic resonant structure 21 is connected to the two output ends 23, and the ring-shaped grounding end 24 is also connected to the acoustic resonant structure 21. The input end of the acoustic resonant structure 21 is used to convert radio frequency signals into surface acoustic waves, and the output end of the acoustic resonant structure 21 is used to convert the filtered surface acoustic waves back into electrical signals, completing the signal filtering process.

[0039] Preferably, in this effective acoustic structure, the positional arrangement of the input end 22, the output end 23 and the ring-shaped grounding end 24 satisfies the requirement of interference-free acoustic signal transmission.

[0040] S2. A separation layer 3 is formed on the side of the effective acoustic structure away from the substrate 1, so that the separation layer 3 completely covers the effective acoustic structure, and an electrical connection window 31 is etched through the separation layer 3; wherein, the thickness of the separation layer 3 is 5~25nm. Specifically, when the thickness of the separation layer 3 is less than 5nm, the overall thickness is too thin to form reliable electrical isolation between the upper and lower metal layers. When the thickness of the separation layer 3 is greater than 25nm, the overall thickness is too thick, which will increase the difficulty of subsequent processes such as photolithography. Therefore, when the thickness of the separation layer 3 is 5~25nm, it has good electrical isolation and improves production efficiency.

[0041] S3. A connecting layer 4 is formed on the side of the separation layer 3 away from the effective acoustic structure. The connecting layer 4 completely covers the separation layer 3 and passes through the electrical connection window 31 to connect with the annular grounding terminal 24 of the acoustic layer 2, thus obtaining an acoustic filter 100; wherein the metal thickness of the connecting layer 4 is the same as the thickness of the acoustic layer 2. Figure 4 As shown, region A is the ring-shaped grounding terminal 24, region B is the first part of acoustic layer 2, and region C is the second part of acoustic layer 2.

[0042] Specifically, an acoustic layer 2 is fabricated on the surface of the substrate 1, and an effective acoustic structure, including an acoustic resonant structure 21, an input end 22, an output end 23, and a ring-shaped grounding end 24, is formed on the acoustic layer 2. A separation layer 3 is formed on the side of the effective acoustic structure away from the substrate 1, so that the separation layer 3 completely covers the effective acoustic structure, and an electrical connection window 31 is etched through the separation layer 3. A connection layer 4 is fabricated on the separation layer 3 to connect the connection layer 4 to the ring-shaped grounding end 24 of the acoustic layer 2, thus obtaining an acoustic filter 100. The metal thickness of the connection layer 4 is the same as that of the acoustic layer 2. In this way, by separating the input, output signals, and ring-shaped grounding end 24 of the complex acoustic device through the thin passivated separation layer 3, the device area is significantly reduced without affecting the performance of the surface acoustic wave filter, achieving miniaturization of the filter device and further improving the overall performance of the filter device. In addition, by optimizing the interlayer structure (without bridging), the chip area is reduced. At the same time, by connecting the layer 4 directly to the ground and separating the layer 3 with precise etching, the sound transmission efficiency of the substrate 1 and the energy concentration of the acoustic resonant structure 21 are ensured, ultimately achieving a balance between miniaturization and high performance.

[0043] In this embodiment, in step S1, the acoustic layer 2 is made of aluminum or a copper-aluminum alloy. Aluminum or copper-aluminum alloys retain the process compatibility of aluminum while incorporating the low resistance advantage of copper, thus meeting the filtering requirements of 5G multi-band and high-performance applications.

[0044] In this embodiment, the effective acoustic structure is fabricated through metal deposition and patterning processes. Metal deposition is performed using physical vapor deposition (PVD, such as sputtering or evaporation) or chemical vapor deposition (CVD) to uniformly deposit an acoustic layer 2 on the surface of substrate 1, with precise control over the film thickness. The deposited passivation layer film exhibits good uniformity, strong adhesion, and stable resistivity, providing a continuous material substrate for subsequent patterning while ensuring the conductivity of the electrodes (reducing signal transmission loss) and mechanical strength. The patterning process involves photolithography, etching, and resist removal. The continuous metal film can be etched into independent input terminals 22, output terminals 23, and a ring-shaped ground terminal 24, with clear boundaries and controllable spacing between components (e.g., interdigital spacing can be precise to the nanometer level), avoiding short circuits or signal crosstalk.

[0045] In this embodiment, in step S2, the etching process of the electrical connection window 31 is either dry etching or wet etching. Dry etching utilizes plasma to physically bombard or chemically react with the material of the separation layer 3, thereby removing the material in the target area. This dry etching method offers extremely high etching precision, suitable for micro / nano window sizes; the window edges are steep and the surface is smooth, ensuring interconnect reliability. Wet etching utilizes a chemical etching solution to selectively react with the material of the separation layer 3, dissolving and removing the material in the target area. This method offers fast etching rates and low costs, suitable for simple window designs; the surface is smooth and undamaged, ensuring contact stability.

[0046] In this embodiment, the thickness of the separation layer 3 is 20 nm. This thickness provides good separation, excellent electrical isolation, and improved production efficiency.

[0047] In this embodiment, in step S2, the separation layer 3 is fabricated using chemical vapor deposition or physical vapor deposition. The deposited metal film exhibits good uniformity, strong adhesion, and stable resistivity, providing a continuous material substrate for subsequent patterning while ensuring the conductivity (reducing signal transmission loss) and mechanical strength of the electrodes.

[0048] In this embodiment, in step S3, the connection layer 4 and the annular grounding terminal 24 are connected via direct metal-to-metal contact. This direct metal-to-metal connection between the connection layer 4 and the annular grounding terminal 24 achieves optimal grounding performance with a minimalist structure; structurally, it supports a bridging-free design, reduces chip area, and simplifies the manufacturing process. Electrically, it reduces grounding resistance and parasitic parameters, suppresses interference, and ensures signal integrity.

[0049] In this embodiment, the graphical structure of the connection layer 4 corresponds to the position of the electrical connection window 31. Precisely matching the graphical design of the connection layer 4 with the position of the electrical connection window 31 ensures the stability of signal transmission.

[0050] In this embodiment, the substrate 1 is made of a piezoelectric material. The piezoelectric material is lithium tantalate (LiTaO3), lithium niobate (LiNbO3), quartz, etc. Its core characteristic is the electromechanical coupling effect. When a radio frequency electrical signal is passed into the acoustic resonance structure 21 of the acoustic layer 2, the substrate 1 will convert electrical energy into mechanical energy and excite surface acoustic waves propagating along the surface of the substrate 1.

[0051] Example 2

[0052] like Figures 2-8 As shown, this embodiment of the invention provides an acoustic filter 100, which is fabricated using the aforementioned acoustic filter fabrication method. By separating the input signal, output signal, and ring ground terminal 24 of the complex acoustic device through a thin passivated separation layer 3, the device area is significantly reduced without affecting the performance of the surface acoustic wave filter, achieving miniaturized filter device design and further improving the overall performance of the filter device. That is, while reducing the chip area, the acoustic filter 100 ensures that the insertion loss, bandwidth, and out-of-band rejection performance of the filter are not reduced.

[0053] It should be noted that the various embodiments described above with reference to the accompanying drawings are merely illustrative of the present invention and not intended to limit its scope. Those skilled in the art should understand that any modifications or equivalent substitutions made to the present invention without departing from its spirit and scope should be included within the scope of the present invention. Furthermore, unless the context otherwise requires, words appearing in the singular include those in the plural, and vice versa. Additionally, unless specifically stated otherwise, all or part of any embodiment may be used in conjunction with all or part of any other embodiment.

Claims

1. A method for fabricating an acoustic filter, characterized in that, The preparation method includes the following steps: S1. A substrate is provided, an acoustic layer is formed on the surface of the substrate, and an effective acoustic structure is formed using the acoustic layer; wherein, the effective acoustic structure includes an acoustic resonant structure, an input end, an output end, and a ring-shaped grounding end, the input end and the output end are respectively connected to opposite ends of the acoustic resonant structure, and the ring-shaped grounding end is arranged around the acoustic resonant structure; S2. A separation layer is formed on the side of the effective acoustic structure away from the substrate, such that the separation layer completely covers the effective acoustic structure, and an electrical connection window is etched through the separation layer; wherein the thickness of the separation layer is 5~25nm; S3. A connecting layer is formed on the side of the separation layer away from the effective acoustic structure, so that the connecting layer completely covers the separation layer, and the connecting layer passes through the electrical connection window and is connected to the ring-shaped ground terminal of the acoustic layer to obtain an acoustic filter; wherein, the thickness of the connecting layer is the same as the thickness of the acoustic layer.

2. The method for fabricating an acoustic filter according to claim 1, characterized in that, In step S1, the acoustic layer is made of aluminum or a copper-aluminum alloy.

3. The method for fabricating an acoustic filter according to claim 1, characterized in that, The effective acoustic structure is fabricated using a metal deposition and patterning process.

4. The method for fabricating an acoustic filter according to claim 1, characterized in that, In step S2, the etching process of the electrical connection window is carried out by dry etching or wet etching.

5. The method for fabricating an acoustic filter according to claim 1, characterized in that, The thickness of the separation layer is 20 nm.

6. The method for fabricating an acoustic filter according to claim 1, characterized in that, In step S2, the separation layer is formed by chemical vapor deposition or physical vapor deposition.

7. The method for fabricating an acoustic filter according to claim 1, characterized in that, In step S3, the connection layer is connected to the annular grounding terminal through direct metal contact.

8. The method for fabricating an acoustic filter according to claim 1, characterized in that, The graphical structure of the connection layer corresponds to the position of the electrical connection window.

9. The method for fabricating an acoustic filter according to claim 1, characterized in that, The substrate is made of a piezoelectric material.

10. An acoustic filter, characterized in that, The acoustic filter is prepared by the method of any one of claims 1-9.

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