Film bulk acoustic resonator with high quality factor and preparation method thereof
By setting a longitudinally concave transverse acoustic reflection structure on the top electrode of the thin-film bulk acoustic resonator, the problems of transverse acoustic loss and spurious modes are solved, achieving filter performance with high quality factor and low in-band insertion loss.
Patent Information
- Application Number
- CN202511557084.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-10-29
- Publication Date
- 2026-01-23
AI Technical Summary
Traditional thin-film bulk acoustic resonators generate longitudinal and transverse acoustic waves during excitation, leading to transverse acoustic wave loss and increased spurious modes, which affect the in-band ripple and signal loss of the filter.
A longitudinally concave transverse acoustic reflection structure is set on the top electrode. By adjusting the angle of the longitudinal concave surface, the reflected sound waves are refracted along different interfaces and concentrated back to the center of the piezoelectric material, thereby suppressing transverse acoustic wave leakage and avoiding stray modes.
This improved the resonator's quality factor Q, enhanced the RF chip's ability to resist interference from signals of similar frequencies, reduced in-band insertion loss, and increased power capacity.
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Figure CN121396128A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The application belongs to the field of third-generation semiconductor technology and radio frequency front-end devices, and particularly relates to a high-quality-factor thin film bulk acoustic resonator and a preparation method thereof. BACKGROUND
[0002] With the rapid development of communication technology, the communication frequency bands of traditional 4G, 5G and future 6G communication technology are facing an increasingly crowded development situation. Especially in the golden frequency band of 2-5 GHz, the communication frequency bands of major communication manufacturers are distributed. In order to avoid mutual interference of communication signals, higher requirements are put forward for the out-of-band suppression of radio frequency filters. The thin film bulk acoustic resonator has the advantages of miniaturization, low in-band insertion loss, high out-of-band suppression and high power capacity, and has become one of the main development directions of filters.
[0003] The traditional thin film bulk acoustic resonator will generate longitudinal acoustic waves (piston mode) and transverse acoustic waves (transverse mode) when excited. The transverse mode and the mixing product of the high-order harmonic will cause acoustic energy leakage and reduce the quality factor Q of the resonator. Although a series of acoustic wave reflection structures have been developed to control the dispersion mode of acoustic waves, including a series of edge pattern boundary structures such as groove structures and protrusion structures at the edges of the electrodes, to suppress the transverse acoustic wave loss of the resonator. However, this additional transverse acoustic wave mode will introduce an additional vibration mode near the resonant frequency, which will increase the spurious mode and affect the in-band ripple of the filter, resulting in signal loss. SUMMARY
[0004] The embodiments of the application provide a high-quality-factor thin film bulk acoustic resonator and a preparation method thereof to solve the problems in the related art. The technical solutions are as follows: In a first aspect, the embodiments of the application provide a high-quality-factor thin film bulk acoustic resonator, which comprises, in sequence: a silicon substrate, a cavity is formed in the center of the substrate; a support layer, a bottom electrode and a piezoelectric layer; a patterned top electrode is arranged on the piezoelectric layer; a transverse acoustic reflection structure is further arranged on the top electrode; the transverse acoustic reflection structure is a concave-shaped pattern combination structure arranged in the top electrode; and the concave-shaped pattern combination structure is filled or not filled.
[0005] In an embodiment, the depth of the cavity is 2-4 μm.
[0006] In an embodiment, the concave-shaped pattern combination structure is filled with any one of tungsten or silicon dioxide.
[0007] In an embodiment, the support layer is one or a combination of Si3N4 or SiC.
[0008] In one embodiment, the thickness of the support layer is 0.05 μm-3 μm.
[0009] In one embodiment, the piezoelectric layer is any one of AlN, Al x Ga 1-x N, Sc x Al 1-x N, Al x Si 1-x N.
[0010] In one embodiment, the thickness of the piezoelectric layer is 0.5 μm-3 μm.
[0011] In one embodiment, the bottom electrode and the top electrode are any one or a combination of two or more of Al, Pt, Nb and Hf.
[0012] In one embodiment, the thickness of the bottom electrode and the top electrode is 0.05 μm-0.5 μm.
[0013] In one embodiment, the patterned top electrode is a regular hexagon.
[0014] In one embodiment, the concave patterned structure includes six grooves arranged in the patterned top electrode.
[0015] In one embodiment, the width of the six grooves is 0.1 μm-5 μm; and the depth is 0.05 μm-0.5 μm.
[0016] In one embodiment, each groove is parallel to each side of the top electrode; the length of the groove is 85%-95% of the length of the side of the top electrode; and the six grooves are connected to form a hexagon.
[0017] In one embodiment, each groove is parallel to each side of the top electrode; the length of the groove is 40%-80% of the length of the side of the top electrode.
[0018] In one embodiment, the angle between each groove and the side of the top electrode is 15-40°; and the length of the groove is 20%-30% of the length of the side of the top electrode.
[0019] In a second aspect, the embodiments of the present application provide a method for preparing a high-quality thin film bulk acoustic resonator, comprising the following steps: (1) growing a sacrificial layer on the surface of a Si wafer substrate; and then growing a support layer on the surface of the substrate; (2) growing a bottom electrode on the support layer, and then growing a piezoelectric layer; (3) growing a patterned top electrode on the surface of the piezoelectric layer, and forming a patterned lateral acoustic reflection structure; (4) Remove the sacrificial layer to form a cavity; obtain the thin film bulk acoustic resonator with the high quality factor.
[0020] In one embodiment, the step of growing the sacrificial layer is as follows: etching a cavity on a substrate and growing a sacrificial layer inside the cavity; the sacrificial layer is one of SiO2 or Si3N4 or a mixture of both.
[0021] In one embodiment, an etching method is used to remove the sacrificial layer; the etching is dry etching with chlorine or fluorine halide gases or wet etching with chlorine or fluorine halide liquids.
[0022] In one embodiment, a sacrificial layer, a bottom electrode, a piezoelectric layer, and a top electrode are grown using a PVD method; and a support layer is grown using plasma-enhanced CVD technology.
[0023] The advantages or beneficial effects of the above technical solutions include at least the following: The high-quality-factor thin-film bulk acoustic resonator of this invention includes a longitudinally concave transverse acoustic reflection structure disposed on the top electrode. By adjusting the angle of the longitudinal concave surface, the reflected sound waves are concentrated at the concave interface, and reflected and concentrated back to the center of the piezoelectric material along different refraction angles at different interfaces. This effectively suppresses energy leakage caused by transverse acoustic waves and simultaneously reflects the sound waves back to the center of the piezoelectric thin film, avoiding the formation of transverse stray sound waves and improving the quality factor Q of the resonator. It also avoids the introduction of stray modes during the suppression of transverse acoustic wave leakage. This effectively enhances the technical guarantee for preventing mutual interference between signals of similar frequencies in the RF chip.
[0024] The above overview is for illustrative purposes only and is not intended to be limiting in any way. In addition to the illustrative aspects, embodiments, and features described above, further aspects, embodiments, and features of this application will become readily apparent from the accompanying drawings and the following detailed description. Attached Figure Description
[0025] In the accompanying drawings, unless otherwise specified, the same reference numerals throughout the various drawings denote the same or similar parts or elements. These drawings are not necessarily drawn to scale. It should be understood that these drawings depict only some embodiments disclosed in this application and should not be construed as limiting the scope of this application.
[0026] Figure 1 This is a schematic diagram of the resonator structure in Example 1; Figure 2 This is a schematic diagram of the preparation process in Example 1; Figure 3 This is a schematic diagram of the top electrode structure of the resonator in Example 1; Figure 4This is a three-dimensional schematic diagram of the longitudinal concave shape of the transverse structural region of the resonator in Example 1, magnified. Figure 5 This is a schematic diagram of the second type of top electrode with a transverse acoustic reflection structure in this invention; Figure 6 This is a schematic diagram of the third type of top electrode with a transverse acoustic reflection structure in this invention.
[0027] Figure 7 This is a Q-value curve of the resonator prepared in the comparative example of this invention.
[0028] Figure 8 This is a Q-value curve of the resonator prepared in Example 1 of the present invention.
[0029] Figure 9 This is a Q-value curve of the resonator prepared in Example 2 of the present invention.
[0030] Figure 10 This is a Q-value curve of the resonator prepared in Example 3 of the present invention. Detailed Implementation
[0031] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of this application. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.
[0032] This application provides a high-quality thin-film bulk acoustic resonator, the resonator comprising a silicon substrate, a cavity, a support layer, a bottom electrode, a piezoelectric layer, a top electrode, and a lateral acoustic reflection structure; A cavity is formed in the center of the silicon substrate; a support layer, a bottom electrode, a piezoelectric layer, and a top electrode are sequentially disposed on the silicon substrate. The top electrode is a patterned electrode; a lateral acoustic reflection structure is also provided inside the top electrode.
[0033] The transverse acoustic reflection structure is a concave graphic combination structure disposed in the top electrode; the structure is a longitudinal concave structure on the top electrode; the longitudinal concave structure is etched on the top electrode; as one embodiment, the longitudinal concave structure is multiple grooves.
[0034] In one embodiment, the concave graphic structure may or may not be filled. In this embodiment, the concave graphic structure is filled with either tungsten metal or silicon dioxide. When the concave graphic structure is not filled with tungsten metal or silicon dioxide, it can be considered that the concave graphic structure is either not filled or filled with air.
[0035] By utilizing materials with different acoustic impedances and patterning them into a longitudinally concave transverse acoustic reflection structure, transverse acoustic waves formed at the concave interface can be concentrated and reflected along different refraction angles at different interfaces, converging back to the center of the piezoelectric material. This effectively suppresses energy leakage caused by transverse acoustic waves and reflects the sound waves back to the center of the piezoelectric thin film, avoiding the formation of transverse stray sound waves. This effectively improves the quality factor Q of the thin-film bulk acoustic resonator, thus laying the foundation for the fabrication of filters with high out-of-band suppression and low in-band insertion loss.
[0036] Compared to traditional transverse acoustic wave reflection structures with concave and convex boundaries, transverse acoustic reflection structures offer a more stable device structure, resulting in a more uniform force distribution within the device. This can improve the out-of-band rejection of filters, reduce in-band insertion loss, and increase the power capacity of the device.
[0037] In one embodiment, the patterned top electrode is a regular hexagon.
[0038] As one implementation, the concave graphic assembly structure includes six grooves disposed within the patterned top electrode.
[0039] In one embodiment, each groove is parallel to each side of the top electrode; the length of the groove is 85%-95% of the side length of the top electrode; the six grooves are connected to form a hexagon. In this embodiment, the six grooves are connected to form a regular hexagon, and the sides of the regular hexagon are parallel to the sides of the resonator.
[0040] In one embodiment, each groove is parallel to each side of the top electrode; the length of the groove is 40%-80% of the side length of the top electrode. In this embodiment, each of the six grooves is parallel to one side of the resonator and located in the middle, such that adjacent grooves are equidistant.
[0041] In one embodiment, each groove forms an angle of 15-40° with the edge of the top electrode; the length of the groove is 20%-30% of the length of the edge of the top electrode. In this embodiment, the six grooves are located at the vertices of the regular hexagonal top electrode, forming an angle of 15-40° with the edge.
[0042] In one embodiment, the width of the six grooves is 0.1μm-5μm, and the depth is 0.05μm-0.5μm.
[0043] In one implementation method, the cavity depth is 2-4 μm.
[0044] As one embodiment, the support layer is a combination of one or both of Si3N4 and SiC.
[0045] In one embodiment, the thickness of the support layer is 0.05μm-3μm.
[0046] As one implementation method, the piezoelectric layer is AlN or Al x Ga 1-x N, Sc x Al 1-x N, Al x Si 1-x Any of N.
[0047] In one embodiment, the thickness of the piezoelectric layer is 0.5μm-3μm.
[0048] As one embodiment, Al, Pt, Nb, or Hf are used in combination of any one or two or more of them.
[0049] In one embodiment, the thicknesses of the bottom electrode and the top electrode are 0.05 μm and 0.5 μm, respectively.
[0050] This application also provides a method for fabricating a high-quality thin-film bulk acoustic resonator, comprising the following steps: (1) A sacrificial layer is grown on the surface of a Si wafer substrate; then a support layer is grown on the surface of the substrate. (2) A bottom electrode is grown on the support layer, and then a piezoelectric layer is grown; (3) A patterned top electrode is grown on the surface of the piezoelectric layer, and a patterned transverse acoustic reflection structure is formed; (4) Remove the sacrificial layer to form a cavity; obtain the thin film bulk acoustic resonator with the high quality factor.
[0051] In one embodiment, the step of growing the sacrificial layer is as follows: etching a cavity on the substrate and growing a sacrificial layer in the cavity; the sacrificial layer is one of SiO2 or Si3N4 or a mixture of both.
[0052] As one implementation method, the sacrificial layer is removed by etching; the etching is dry etching with chlorine or fluorine halide gases or wet etching with chlorine or fluorine halide liquids.
[0053] As one implementation method, a sacrificial layer, a bottom electrode, a piezoelectric layer, and a top electrode are grown using PVD; and a support layer is grown using plasma-enhanced CVD technology.
[0054] As one implementation method, the patterned transverse acoustic reflection structure is formed by etching a longitudinal concave structure through photolithography, wet chemical etching, or dry etching to form a patterned transverse acoustic reflection structure.
[0055] The following is a further explanation using specific embodiments.
[0056] Example 1 A high-quality thin-film bulk acoustic resonator and its fabrication method, wherein the resonator is as follows: Figure 1 As shown, it includes a silicon substrate 101, a cavity 102, a support layer 103, a bottom electrode 104, a piezoelectric layer 105, a top electrode 106, and a lateral acoustic reflection structure 107. Both the bottom electrode and the top electrode are made of molybdenum, and the lateral acoustic reflection structure is filled with tungsten. The thickness of both the bottom electrode and the top electrode is 500 nm, and the thickness of the piezoelectric layer is 1 μm. The preparation method includes the following steps, as follows: Figure 2 As shown: (1) Select (111) Si wafer as substrate 101, clean and dry the substrate with acetone and hydrofluoric acid; prepare a 3 μm deep cavity on the surface of the silicon substrate by plasma etching. (2) An amorphous silicon sacrificial layer 108 was grown by PVD with a thickness of 3.1 μm. The sacrificial layer was then polished and a Si3N4 material was grown as a support layer 104 with a thickness of 50 nm by plasma-enhanced CVD. (4) A 500 nm thick layer of metallic Mo is deposited on the surface of the sacrificial layer using PVD as the bottom electrode 104, and AlN is grown on the metallic Mo using PVD as the piezoelectric layer 105 with a thickness of 1 μm. (5) A 500 nm thick layer of metallic Mo is deposited on the surface of the piezoelectric layer 105 using PVD as the top electrode 106; (6) A longitudinal concave structure is etched on the top electrode metal Mo using a dry etching method, and metal W is grown using PVD to fill the etched structure completely, forming a transverse acoustic reflection structure, such as... Figure 3 As shown; (7) Removing the sacrificial layer material by dry etching: The above resonator is placed in gaseous hydrogen fluoride to release the amorphous silicon sacrificial layer 107, and the sacrificial layer material is removed by dry etching, thereby preparing the resonator.
[0057] Example 2 The difference between Example 2 and Example 1 is that the preparation method is as follows: Figure 5 The transverse acoustic reflection structure shown in the figure is the same as the other methods and steps.
[0058] Example 3 The difference between Example 3 and Example 1 is that the preparation method is as follows: Figure 6 The transverse acoustic reflection structure shown in the figure is the same as the other methods and steps.
[0059] Comparative Example 1 The difference between Comparative Example 1 and the embodiment is that the transverse acoustic reflection structure is not etched, but a conventional transverse concave-convex boundary transverse acoustic wave reflection structure is used, while the other methods and steps are the same.
[0060] The Q-value curve of the resonator prepared in Example 1 of this invention is shown in the figure below. Figure 8 As shown in the figure, the Q-value curve of the resonator prepared in Example 2 is as follows. Figure 9 As shown, the Q-value curve of the resonator prepared in Example 3 is as follows. Figure 10 As shown; the Q-value curve of the resonator prepared in Comparative Example 1 is shown in Figure 1. Figure 7 As shown.
[0061] from Figures 7-10 It can be seen that the resonator fabricated using the traditional metal electrode boundary ring structure in Comparative Example 1 can only achieve a maximum Q value of 3039, while the resonator using the transverse acoustic reflection structure of this invention can achieve a Q value of over 4000, and even up to 5000. Furthermore, the curve clearly shows that the Q value fluctuation in the stray mode region of the resonator is much smaller than that of the comparative example, indicating that the transverse acoustic reflection structure has a good suppression effect on the parasitic vibrations of the resonator.
[0062] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of those different embodiments or examples.
[0063] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "a plurality of" means two or more, unless otherwise explicitly specified.
[0064] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various variations or substitutions within the technical scope disclosed in this application, and these should all be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.
Claims
1. A high-quality thin-film bulk acoustic resonator, characterized in that, Including the following settings in sequence: A silicon substrate, wherein a cavity is formed in the center of the substrate; The structure comprises a support layer, a bottom electrode, and a piezoelectric layer; a patterned top electrode is provided on the piezoelectric layer; a lateral acoustic reflection structure is also provided on the top electrode; the lateral acoustic reflection structure is a concave pattern combination structure disposed within the top electrode; the concave pattern combination structure may be filled or unfilled.
2. The high-quality factor thin-film bulk acoustic resonator according to claim 1, characterized in that, The depth of the cavity is 2-4 μm; The concave graphic combination structure is filled with either tungsten or silicon dioxide. The support layer is a combination of one or both of Si3N4 and SiC; the thickness of the support layer is 0.05μm-3μm; The piezoelectric layer is AlN, Al x Ga 1-x N, Sc x Al 1-x N, Al x Si 1-x Any one of N; the thickness of the piezoelectric layer is 0.5μm-3μm; The bottom electrode and the top electrode are any one or a combination of two or more of Au, Ag, Ru, W, Mo, Ir, Al, Pt, Nb, and Hf, respectively; the thickness of the bottom electrode and the top electrode are 0.05 μm to 0.5 μm, respectively.
3. A high-quality thin-film bulk acoustic resonator according to claim 1, characterized in that, The patterned top electrode is a regular hexagon; the concave patterned combination structure includes six grooves disposed within the patterned top electrode; The width of the six grooves is 0.1μm-5μm; the depth is 0.05μm-0.5μm.
4. A high-quality thin-film bulk acoustic resonator according to claim 3, characterized in that, Each groove is parallel to each side of the top electrode; the length of the groove is 85%-95% of the side length of the top electrode; the six grooves are connected to form a hexagon.
5. A high-quality thin-film bulk acoustic resonator according to claim 3, characterized in that, Each groove is parallel to each side of the top electrode; the length of the groove is 40%-80% of the side length of the top electrode.
6. A high-quality thin-film bulk acoustic resonator according to claim 3, characterized in that, Each groove forms an angle of 15-40° with the edge of the top electrode; the length of the groove is 20%-30% of the length of the edge of the top electrode.
7. A method for fabricating a high-quality thin-film bulk acoustic resonator according to any one of claims 1-6, characterized in that, Includes the following steps: (1) A sacrificial layer is grown on the surface of a Si wafer substrate; then a support layer is grown on the surface of the substrate. (2) A bottom electrode is grown on the support layer, and then a piezoelectric layer is grown; (3) A patterned top electrode is grown on the surface of the piezoelectric layer, and a patterned transverse acoustic reflection structure is formed; (4) Remove the sacrificial layer to form a cavity; A thin-film bulk acoustic resonator with the aforementioned high quality factor is obtained.
8. The method for fabricating a high-quality thin-film bulk acoustic resonator according to claim 7, characterized in that, The steps for growing the sacrificial layer are as follows: etching a cavity on the substrate and growing a sacrificial layer inside the cavity; the sacrificial layer is one of SiO2 or Si3N4 or a mixture of both.
9. The method for fabricating a high-quality thin-film bulk acoustic resonator according to claim 7, characterized in that, The sacrificial layer is removed by etching; the etching is dry etching with chlorine or fluorine halide gases or wet etching with chlorine or fluorine halide liquids.
10. The method for fabricating a high-quality thin-film bulk acoustic resonator according to claim 7, characterized in that, The sacrificial layer, bottom electrode, piezoelectric layer and top electrode were grown using PVD; the support layer was grown using plasma-enhanced CVD.