A ring bulk acoustic resonator and a method of manufacturing the same

Abstract

This invention provides a ring-shaped bulk acoustic wave resonator and its fabrication method, comprising a substrate, a piezoelectric stack structure, a mass load structure, a connecting wire structure, and a pad structure. The substrate has a cavity; the piezoelectric stack structure is a ring-shaped structure with a central cutout, comprising a bottom electrode, a piezoelectric layer, and a top electrode sequentially from bottom to top. The piezoelectric stack structure is suspended above the cavity and is not connected to the sidewalls of the cavity; the connecting wire structure is a curved, serpentine shape; the pad structure is connected to the substrate, and the piezoelectric stack structure is connected to the pad structure via the connecting wire structure. Because the piezoelectric stack structure is ring-shaped with a central cutout, the cavity can be directly etched from the cutout, eliminating the need for pre-etching cavity release holes, resulting in higher efficiency and reducing the probability of incomplete cavity release affecting resonator performance. The serpentine shape of the connecting wire structure allows it to bend, stretch, and twist in different directions, enhancing the resonator's ductility and sensitivity.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor device technology, and particularly relates to a ring-shaped bulk acoustic resonator and its fabrication method. Background Technology

[0002] With the advent of the 5G / 6G era, wireless communication is developing towards higher communication frequencies, higher transmission rates, higher density multiplexing, and higher integration. Traditional surface acoustic wave (SAW) resonators, due to their inherent structural limitations, are not suitable for higher frequency signal transmission. In contrast, thin-film bulk acoustic wave (TIW) resonators offer advantages such as small size, low insertion loss, higher power capacity, and the ability to achieve higher communication frequencies. They are also compatible with CMOS, meeting the demands of device integration. Therefore, TAW resonators have gradually become a hot topic in the field of radio frequency (RF) filter research.

[0003] In related technologies, thin-film bulk acoustic wave resonators mainly consist of a substrate, a top electrode, a piezoelectric layer, a bottom electrode, a cavity, and cavity release holes. During fabrication, the cavity release holes must be etched first, followed by etching the cavity through the release holes. This method is cumbersome and may result in incomplete release at the cavity edges, thus affecting resonator performance. The resonant frequency of a thin-film bulk acoustic wave resonator is primarily determined by the film thickness of the electrode and piezoelectric layers. This necessitates strict control of the film thickness during fabrication; the film thickness uniformity across the entire wafer must be less than 0.1% to achieve high consistency and yield. Therefore, simplifying the resonator fabrication process, improving resonator performance, increasing device yield, and reducing process costs have become pressing technical challenges. Summary of the Invention

[0004] The purpose of this invention is to provide a ring-shaped solid acoustic resonator and its fabrication method, which can simplify the fabrication steps of the resonator and improve the device yield and process cost.

[0005] To achieve the above objectives, the present invention provides a ring-shaped bulk acoustic resonator.

[0006] A ring-shaped bulk acoustic resonator, comprising:

[0007] A substrate with cavities formed thereon;

[0008] The piezoelectric stacked structure is a ring structure with a hollow center. From bottom to top, it includes a bottom electrode, a piezoelectric layer, and a top electrode. The piezoelectric stacked structure is suspended above the cavity and is not in contact with the side wall of the cavity.

[0009] The connecting line structure is a curved, serpentine shape;

[0010] The pad structure is connected to the substrate;

[0011] The piezoelectric stack structure is connected to the pad structure through a connecting wire structure. The connecting wire structure serves both as an electrical connection and as a support for the piezoelectric stack structure, keeping it suspended.

[0012] The aforementioned ring-shaped bulk acoustic resonator further includes a mass load structure, which is connected to the upper edge of the top electrode and is ring-shaped.

[0013] The aforementioned ring-shaped acoustic resonator has a ring structure that is circular, a regular polygonal ring, or an irregular polygonal ring.

[0014] In the aforementioned ring-shaped acoustic resonator, the piezoelectric layer and the piezoelectric material layer are made of aluminum nitride, scandium-doped aluminum nitride, lithium niobate, potassium niobate, lithium tantalate, zinc oxide, lead zirconate titanate, or quartz.

[0015] In the aforementioned ring-shaped solid acoustic resonator, the top and bottom electrodes are made of one or more of the following materials: tungsten, molybdenum, aluminum, gold, and platinum.

[0016] In the aforementioned ring-shaped bulk acoustic resonator, the mass load structure is one or a combination of molybdenum, tungsten, aluminum, gold, and platinum. More preferably, the material of the mass load structure is the same as the material of the top electrode and the bottom electrode.

[0017] In the aforementioned ring-shaped acoustic resonator, the connecting wire structure is bent once or multiple times.

[0018] The aforementioned ring-shaped bulk acoustic resonator includes a connecting wire structure comprising a bottom electrode layer, a piezoelectric material layer, and a top electrode layer. The pad structure includes a signal input pad and a signal output pad. The top electrode and piezoelectric layer of the piezoelectric stack structure are connected to the signal input pad of the pad structure via the top electrode layer and piezoelectric material layer of the connecting wire structure. The bottom electrode of the piezoelectric stack structure is connected to the signal output pad via the bottom electrode layer of the connecting wire structure.

[0019] The aforementioned ring-shaped acoustic resonator further includes a grounding pad in its pad structure.

[0020] The method for fabricating a ring-shaped solid acoustic resonator described in any of the above-mentioned embodiments involves etching a cavity through the hollow area of ​​the ring structure during fabrication, eliminating the need for additional etching of cavity release holes.

[0021] The above-mentioned method for fabricating a ring-shaped acoustic resonator controls the frequency of the resonator by adjusting the inner and outer radii of the ring structure.

[0022] One application of the toroidal bulk acoustic resonator described in any of the above claims is for the manufacture of liquid sensors or accelerometers.

[0023] The advantages of this invention are as follows: In the prior art, the resonant frequency of a thin-film bulk acoustic resonator is mainly determined by the thickness of the piezoelectric layer. This requires strict control of the film thickness during fabrication, with the film thickness uniformity across the entire wafer needing to be less than 0.1% to achieve high consistency and yield. The resonant frequency of the ring resonator described in this invention is determined by the size of the ring region. The frequency of the resonator can be adjusted by changing the inner and outer radii of the ring structure. This reduces the challenges associated with precise control of the film thickness during the manufacturing process, providing a more economical and feasible solution than existing resonators, and holds promise for enabling the mass production of piezoelectric resonator arrays with different frequencies on a single chip.

[0024] Furthermore, the serpentine connecting wire structure has better tensile performance than ordinary connecting wires. It can be bent, stretched, and twisted in different directions, and returns to its original shape after the external force is removed. This increases the maximum displacement range of the resonator, making the resonator more ductile and more sensitive.

[0025] Furthermore, the toroidal acoustic resonator can be used to make accelerometers. Compared with traditional accelerometers, accelerometers based on toroidal acoustic resonators have advantages such as fast response speed, small size, light weight, and low power consumption.

[0026] Furthermore, toroidal volumetric acoustic resonators can be used for liquid sensing, utilizing changes in resonant frequency to measure physical parameters such as liquid density, viscosity, and flow velocity. Compared to traditional liquid sensing technologies, sensors based on toroidal volumetric acoustic resonators offer higher accuracy and sensitivity, making them suitable for demanding applications in industrial automation, biomedicine, and environmental monitoring. It's worth noting that due to the hollow structure of the toroidal resonator, liquid can naturally wet and fill the hollow area. This liquid wetting increases the contact area and degree of contact between the liquid and the resonator, thereby improving the sensor's response and sensitivity.

[0027] Furthermore, toroidal acoustic resonators are smaller in size than traditional resonators, allowing them to be integrated and installed in a smaller space, thereby improving the compactness and flexibility of the system.

[0028] Furthermore, the annular hollow structure can simplify the process steps. By etching the cavity through the hollow area, the sacrificial layer can be released directly without the need for additional cavity release holes.

[0029] Furthermore, the edges of the piezoelectric layer are exposed to the air, forming a natural interface of high and low acoustic impedance, which can effectively suppress the transverse wave loss of the piezoelectric layer and thus improve the Q value of the resonator.

[0030] Furthermore, a mass load can be added to the edge of the annular region to improve the Q value of the resonator. Attached Figure Description

[0031] The accompanying drawings are used to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, and do not constitute an undue limitation on the present invention. Wherein:

[0032] Figure 1 This is a top view of a resonator in the prior art.

[0033] Figure 2 This is a schematic diagram of the overall structure of a ring-shaped acoustic resonator without a mass load according to the present invention.

[0034] Figure 3 This is a top view schematic diagram of a ring-shaped acoustic resonator without a mass load structure according to the present invention.

[0035] Figure 4 This is a cross-sectional structural schematic diagram of a ring-shaped acoustic resonator without a mass load structure according to the present invention.

[0036] Figure 5 This is a schematic diagram of the overall structure of a ring-shaped acoustic resonator with a mass load according to the present invention.

[0037] Figure 6 This is a cross-sectional structural diagram of a ring-shaped acoustic resonator with a mass load structure according to the present invention.

[0038] In the figure: 1-substrate, 101-cavity, 2-piezoelectric stacked structure, 201-top electrode, 202-piezoelectric layer, 203-bottom electrode, 3-connector structure, 301-top electrode layer, 302-piezoelectric material layer, 303-bottom electrode layer, 4-pad structure, 401-signal input pad, 402-signal output pad, 403-ground pad, 5-cavity release hole, 6-mass load structure. Detailed Implementation

[0039] To more clearly illustrate the technical solutions of this invention and / or the prior art, the ring-shaped solid acoustic resonator of this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages and features of this invention will become clearer. It should be noted that the concept of the technical solution of this invention can be implemented in many different forms and is not limited to the specific embodiments described herein. All accompanying drawings are schematic diagrams and use non-precise scales, and are only used to assist in illustrating the purpose of the embodiments of this invention.

[0040] like Figures 2-4The ring-shaped bulk acoustic resonator includes a substrate 1, a piezoelectric stacked structure 2, a connecting line structure 3, and a pad structure 4. A cavity 101 is formed on the substrate 1. The pad structure 4 is connected to the substrate 1 around the cavity 101. The piezoelectric stacked structure 2 is a ring-shaped structure with a central hollow core. The connecting line structure is a curved serpentine line. The piezoelectric stacked structure 2 is connected via the connecting line structure 3 and the pad structure 4, and is suspended above the cavity 101 without contacting the sidewalls of the cavity 101. The piezoelectric stacked structure 2 includes a top electrode 201, a piezoelectric layer 202, and a bottom electrode 203, forming the resonant region. The connection structure 3 includes a bottom electrode layer 303, a piezoelectric material layer 302, and a top electrode layer 301. The pad structure 4 includes a signal input pad 401, a signal output pad 402, and a ground pad 403. The top electrode 201 and piezoelectric layer 202 of the piezoelectric stack structure 2 are connected to the signal input pad 401 of the pad structure 4 through the top electrode layer 301 and piezoelectric material layer 302 of the connection structure 3. The bottom electrode 203 of the piezoelectric stack structure 2 is connected to the signal output pad 402 through the bottom electrode layer 303 of the connection structure 3.

[0041] The hollow structure in the middle of the annular piezoelectric stack structure 2 can be directly used to release the cavity 101. After releasing the cavity 101, the piezoelectric stack structure 2 is suspended on the cavity 101 of the substrate 1. The connecting line structure 3 serves both as a connection and as a support to keep the piezoelectric stack structure 2 suspended.

[0042] like Figure 5 and Figure 6 The resonator structure is similar to Figures 2 to 4 The embodiments shown are basically the same. The difference is that an annular mass load structure 6 is added to the upper edge of the top electrode 201.

[0043] The ring-shaped piezoelectric stack structure 2 is a circular ring, a regular polygonal ring, or an irregular polygonal ring.

[0044] The piezoelectric layer 202 is made of aluminum nitride, scandium-doped aluminum nitride, lithium niobate, potassium niobate, lithium tantalate, zinc oxide, lead zirconate titanate, or quartz.

[0045] The materials of the top electrode 201 and the bottom electrode 203 are one or more of tungsten, molybdenum, aluminum, gold, and platinum.

[0046] The mass load structure 6 is one or more of molybdenum, tungsten, aluminum, gold, and platinum.

[0047] The connecting wires of the bottom electrode 203 and the top electrode 201 are bent once or multiple times.

[0048] The mass load structure 6, connected to the edge of the top electrode 201 in a ring shape, can effectively suppress the transverse wave loss of the piezoelectric layer 202, thereby improving the Q value of the resonator. The Q value is the quality factor, which is one of the important indicators for evaluating the performance of filters and resonators. A high quality factor ensures good in-band insertion loss of the filter.

[0049] like Figure 1 In related technologies, thin-film bulk acoustic wave resonators mainly include a substrate 1, a top electrode 201, a piezoelectric layer 202, a bottom electrode 203, a cavity 101, and a cavity release hole 5. In traditional fabrication, the cavity release hole 5 must be etched first, followed by etching the cavity 101 through the cavity release hole 5. This method is cumbersome and may result in incomplete release at the edges of the cavity 101, thus affecting the resonator's performance. However, in the resonator of this invention, because the piezoelectric stack structure 2 is annular with a hollow center, the cavity 101 can be etched directly from the hollow area, eliminating the need to first etch the cavity release hole 5. This method is more efficient and reduces the probability of incomplete release of the cavity 101 affecting the resonator's performance.

[0050] Furthermore, the resonant frequency of this resonator is determined by the size of the annular region. Therefore, the frequency of the resonator can be controlled by adjusting parameters such as the inner and outer radii of the annular structure. This overcomes the limitations of existing technologies that control the resonant frequency by the thickness of the thin film, reduces the challenges of precise control of the thin film thickness in the manufacturing process, and provides a more economical and feasible solution than existing thin-film bulk acoustic resonators.

[0051] It should be understood that any parts not described in detail in this specification belong to the prior art. Although specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, those skilled in the art should understand that these are merely illustrative examples, and various modifications or variations can be made to these embodiments without departing from the principles and essence of the present invention. The scope of the present invention is defined only by the appended claims.

Claims

1. A ring-shaped bulk acoustic resonator, characterized in that, include: A substrate (1) has a cavity (101) on it. The substrate is used to provide mechanical support for the resonator and make its structure stable. The piezoelectric stacked structure (2) is a ring structure with a central hollow structure, which includes a bottom electrode (203), a piezoelectric layer (202) and a top electrode (201) from bottom to top. The piezoelectric stacked structure (2) is suspended above the cavity (101) and is not in contact with the side wall of the cavity (101). The connecting line structure (3) is a curved serpentine shape; The pad structure (4) is connected to the substrate (1); The piezoelectric stack structure (2) is connected to the pad structure (4) through the connecting line structure (3). The connecting line structure (3) serves both as an electrical connection and as a support for the piezoelectric stack structure (2) to keep it suspended. The connecting line structure (3) includes a bottom electrode layer (303), a piezoelectric material layer (302), and a top electrode layer (301).

2. A ring-shaped solid acoustic resonator as described in claim 1, characterized in that, It also includes a mass load structure (6), which is connected to the edge of the upper surface of the top electrode (201) and is in the form of a ring.

3. A ring-shaped bulk acoustic resonator as described in claim 1, characterized in that, The ring structure is in the shape of a circular ring, a regular polygonal ring, or an irregular polygonal ring.

4. A ring-shaped bulk acoustic resonator as described in claim 1, characterized in that, The piezoelectric layer (202) is made of aluminum nitride, scandium-doped aluminum nitride, lithium niobate, potassium niobate, lithium tantalate, zinc oxide, lead zirconate titanate, or quartz.

5. A ring-shaped bulk acoustic resonator as described in claim 1, characterized in that, The materials of the top electrode (201) and the bottom electrode (203) are one or more combinations of tungsten, molybdenum, aluminum, gold, and platinum.

6. A ring-shaped bulk acoustic resonator as described in claim 2, characterized in that, The mass load structure (6) is one or more of tungsten, molybdenum, aluminum, gold, and platinum.

7. A ring-shaped bulk acoustic resonator as described in claim 1, characterized in that, The connecting line structure (3) is bent once or multiple times.

8. A method for fabricating a ring-shaped bulk acoustic resonator as described in any one of claims 1 to 7, characterized in that, During preparation, the cavity (101) is etched through the hollow area of ​​the annular structure, without the need to reserve a cavity release hole (5).

9. The method for fabricating a ring-shaped solid acoustic resonator as described in claim 8, characterized in that, The frequency of the resonator is controlled by adjusting the inner and outer radii of the ring structure.

10. The use of the ring-shaped bulk acoustic resonator according to any one of claims 1 to 7, characterized in that, Used to make liquid sensors or accelerometers.

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