A film bulk acoustic resonator, a manufacturing method and a filter

Abstract

This application provides a thin-film bulk acoustic wave resonator, its fabrication method, and a filter, relating to the field of resonator technology. By performing nitriding treatment on the surface of the bottom electrode to form a compositionally graded interface transition layer, the abrupt compositional interface between the metal electrode and the piezoelectric material is eliminated, significantly reducing interface scattering and interface loss. This solves the problem of interface loss leading to resonator performance degradation in the prior art, improves the Q value of the thin-film bulk acoustic wave resonator, and thus improves the overall performance of the device.

Description

Technical Field

[0001] This application relates to the field of resonator technology, and more specifically, to a thin-film bulk acoustic resonator, its fabrication method, and a filter. Background Technology

[0002] To meet the performance requirements of BAW filters in future communications, it is necessary to further suppress BAW filter losses. BAW filter losses can be divided into volume losses and interface losses. Currently, mainstream research focuses on volume losses, including improving the quality of piezoelectric materials and constructing acoustic reflection structures. However, with increasing operating frequencies and more stringent performance requirements, interface losses further exacerbate the performance degradation of devices. Specifically, the interface loss of BAW resonators mainly stems from the abrupt interface between the metal electrodes and piezoelectric materials, leading to performance deterioration.

[0003] There is currently no effective technical solution to the above problems. Summary of the Invention

[0004] The purpose of this application is to provide a thin-film bulk acoustic resonator, its fabrication method, and a filter. This significantly reduces interface scattering and interface loss, solving the problem of resonator performance degradation caused by interface loss in existing technologies, improving the Q value of the thin-film bulk acoustic resonator, and thus improving the overall performance of the device.

[0005] In a first aspect, this application provides a method for fabricating a thin-film bulk acoustic resonator, wherein a nitriding treatment is performed on the surface of the bottom electrode of the thin-film bulk acoustic resonator to form an interface transition layer on the surface of the bottom electrode. A piezoelectric layer is prepared on the interface transition layer, and the top electrode of the thin-film bulk acoustic resonator is prepared on the piezoelectric layer; After the top electrode is fabricated, the sacrificial layer in the thin-film bulk acoustic resonator is etched to obtain the thin-film bulk acoustic resonator.

[0006] The above solution can significantly reduce interface scattering and interface loss, solve the problem of interface loss causing resonator performance degradation in the prior art, improve the Q value of thin-film bulk acoustic resonators, and thus improve the overall performance of the device.

[0007] Optionally, the nitriding treatment on the bottom electrode surface of the thin-film bulk acoustic resonator to form an interface transition layer on the bottom electrode surface includes: Radio frequency sputtering is used to back-sputter nitrogen atoms onto the surface of the bottom electrode to form an interface transition layer on the surface of the bottom electrode; or, A plasma-enhanced chemical vapor deposition process is used to deposit nitride on the surface of the bottom electrode to form an interface transition layer on the surface of the bottom electrode; or, The bottom electrode surface is heat-treated with a nitrogen-containing solution to form an interface transition layer on the bottom electrode surface; or, The bottom electrode surface is heat-treated in an ammonia atmosphere to form an interface transition layer on the bottom electrode surface.

[0008] The solution proposed in this application provides a feasible nitriding process, which makes the formation of the interface transition layer more controllable and efficient, thereby significantly suppressing interface loss and improving the Q value of the thin-film bulk acoustic resonator.

[0009] Optionally, the heat treatment of the bottom electrode surface in an ammonia atmosphere to form an interface transition layer on the bottom electrode surface includes: The bottom electrode surface is placed in an ammonia atmosphere within a preset pressure range, and the bottom electrode surface is heat-treated according to a preset target temperature and holding time to form an interface transition layer on the bottom electrode surface.

[0010] The above method enables the stable formation of a smoothly transitioning interface layer with a gradually changing composition on the surface of the bottom electrode. This interface layer effectively reduces the acoustic impedance mismatch between the bottom electrode and the subsequently grown piezoelectric layer, thereby significantly suppressing acoustic wave scattering and energy loss at the interface.

[0011] Optionally, the fabrication method further includes, before nitriding the surface of the bottom electrode of the thin-film bulk acoustic resonator: A cavity is formed on the substrate of the thin-film bulk acoustic resonator, and the cavity is filled with a sacrificial layer; A support layer is prepared on the substrate and the sacrificial layer; The bottom electrode of the thin-film bulk acoustic resonator is fabricated on the support layer.

[0012] Optionally, the substrate is made of any one of silicon, sapphire, and silicon carbide.

[0013] Optionally, the sacrificial layer is made of at least one of silicon dioxide, amorphous silicon, and phosphosilicate glass; The support layer is silicon nitride and / or silicon carbide.

[0014] Optionally, the etching includes either dry etching or liquid wet etching.

[0015] Optionally, the materials of the top electrode and the bottom electrode are at least one selected from silver, molybdenum, aluminum, niobium and hafnium; The piezoelectric layer is any one of aluminum nitride, aluminum gallium nitride, scandium aluminum nitride, and aluminum silicon nitride.

[0016] In a second aspect, this application provides a thin-film bulk acoustic resonator, comprising: a substrate, a support layer, a bottom electrode, an interface transition layer, a piezoelectric layer, and a top electrode stacked sequentially. The interface transition layer is a transition layer obtained by nitriding the surface of the bottom electrode of the thin-film bulk acoustic resonator.

[0017] Thirdly, this application provides a filter, including: a thin-film bulk acoustic resonator, said thin-film bulk acoustic resonator being prepared by the preparation method described in any of the preceding claims.

[0018] As can be seen from the above, the fabrication method of the thin-film bulk acoustic resonator provided in this application forms a compositionally graded interface transition layer by nitriding the surface of the bottom electrode. This eliminates the abrupt compositional interface between the metal electrode and the piezoelectric material, significantly reducing interface scattering and interface loss. It solves the problem of interface loss causing resonator performance degradation in the prior art, improves the Q value of the thin-film bulk acoustic resonator, and thus improves the overall performance of the device. At the same time, it avoids the introduction of an additional independent interface layer and avoids the secondary scattering problem that may be caused by the new interface, thereby providing a reliable acoustic resonance structure for high-performance communication applications.

[0019] Other features and advantages of this application will be set forth in the following description and will be apparent in part from the description or may be learned by practicing embodiments of this application. The objectives and other advantages of this application may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. Attached Figure Description

[0020] Figure 1 This is a first flowchart of a method for fabricating a thin-film bulk acoustic resonator provided in an embodiment of this application.

[0021] Figure 2 This is a schematic diagram of a thin-film bulk acoustic resonator provided in an embodiment of this application.

[0022] Figure 3 This is a second flowchart illustrating the fabrication method of a thin-film bulk acoustic resonator provided in an embodiment of this application.

[0023] Figure 4 This is a surface topography image of the bottom electrode of a conventional resonator.

[0024] Figure 5 This is the quality factor curve corresponding to a traditional resonator.

[0025] Figure 6 The image shows the surface morphology of the bottom electrode after nitriding, as provided in the embodiments of this application.

[0026] Figure 7The quality factor curve is the corresponding curve of the thin-film bulk acoustic resonator provided in the embodiments of this application.

[0027] Labeling explanations: 101, substrate; 102, cavity; 103, support layer; 104, bottom electrode; 105, piezoelectric layer; 106, top electrode; 107, sacrificial layer; 108, interface transition layer. Detailed Implementation

[0028] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of the embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of this application provided in the accompanying drawings is not intended to limit the scope of the claimed application, but merely represents selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

[0029] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this application, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0030] refer to Figures 1-7 This application provides a method for fabricating a thin-film bulk acoustic resonator, comprising: Step S1: Nitriding treatment is performed on the surface of the bottom electrode 104 of the thin film bulk acoustic resonator to form an interface transition layer 108 on the surface of the bottom electrode 104. Step S2: A piezoelectric layer 105 is prepared on the interface transition layer 108, and the top electrode 106 of the thin film bulk acoustic resonator is prepared on the piezoelectric layer 105. Step S3: After the top electrode 106 is fabricated, the sacrificial layer 107 in the thin film bulk acoustic resonator is etched to obtain the thin film bulk acoustic resonator.

[0031] The interface transition layer 108 in this application refers to a compositional gradient layer formed on the surface of the bottom electrode 104 by nitriding. The interface transition layer 108 is designed to smooth the material transition between the bottom electrode 104 and the piezoelectric layer 105, thereby reducing interface scattering and loss.

[0032] Sacrificial layer 107: A temporary layer used to support the upper structure during the fabrication of the thin-film bulk acoustic resonator and removed in subsequent processes. By etching the sacrificial layer 107, the cavity 102 structure required for the resonator can be formed.

[0033] Specifically, a nitriding treatment is performed on the surface of the bottom electrode 104 of the thin-film bulk acoustic resonator to form an interface transition layer 108 on the surface of the bottom electrode 104. This nitriding treatment aims to alter the chemical composition and microstructure of the surface of the bottom electrode 104, creating a smooth transition region between it and the subsequently grown piezoelectric layer 105. For example, the surface of the bottom electrode 104 can be exposed to a nitrogen-containing atmosphere, causing nitrogen atoms to react with metal atoms on the surface of the bottom electrode 104 at high temperature, thereby forming a mixed layer of metal nitrides or metal nitrides, which serves as the interface transition layer 108. Another approach is to utilize plasma technology, activating nitrogen gas in a plasma environment to bombard the surface of the bottom electrode 104 with highly reactive nitrogen ions or free radicals, promoting a nitriding reaction. Alternatively, a chemical solution treatment can be used, immersing the bottom electrode 104 in a solution containing a nitrogen source to form a nitrided layer on the surface of the bottom electrode 104 through a chemical reaction, which serves as the interface transition layer 108.

[0034] A piezoelectric layer 105 is fabricated on the interface transition layer 108, and a top electrode 106 of the thin-film bulk acoustic resonator is fabricated on the piezoelectric layer 105. After forming the interface transition layer 108, the piezoelectric layer 105 is deposited on the interface transition layer 108. For example, a physical vapor deposition (PVD) method, such as magnetron sputtering, can be used to deposit a piezoelectric material (such as aluminum nitride) on the interface transition layer 108 to form a piezoelectric thin film with a specific crystal orientation and thickness. Subsequently, the top electrode 106 is fabricated above the piezoelectric layer 105. The fabrication method of the top electrode 106 can be similar to that of the bottom electrode 104, for example, by sputtering a metal thin film and forming the desired electrode pattern through photolithography and etching processes.

[0035] After the top electrode 106 is fabricated, the sacrificial layer 107 in the thin-film bulk acoustic wave resonator is etched to obtain the thin-film bulk acoustic wave resonator. After all functional layers (bottom electrode 104, interface transition layer 108, piezoelectric layer 105, and top electrode 106) are fabricated, the sacrificial layer 107 supporting these layers needs to be removed to form the cavity 102 structure required for the resonator. For example, wet etching can be used, immersing the device in a specific chemical solution that can selectively dissolve the sacrificial layer 107 without damaging other functional layers. Another method is dry etching, such as reactive ion etching (RIE), which uses active particles in plasma to chemically react with or physically bombard the sacrificial layer 107 material to remove the sacrificial layer 107, thereby forming the final thin-film bulk acoustic wave resonator.

[0036] The following example will provide a more detailed explanation of the above technical solution: In conventional thin-film bulk acoustic wave resonators, the piezoelectric layer 105 is typically deposited directly on the metal bottom electrode 104 during fabrication. For example, assuming a thin-film bulk acoustic wave resonator is fabricated on a silicon substrate 101, a molybdenum bottom electrode 104 is first formed on the silicon substrate 101, and then an aluminum nitride piezoelectric layer 105 is deposited directly on the molybdenum bottom electrode 104. Since molybdenum and aluminum nitride are two materials with significantly different properties, there will be a significant lattice mismatch and abrupt chemical bonding at their interface. If these problems are not addressed, when sound waves propagate in the resonator, strong scattering and reflection will occur at this abrupt interface, leading to acoustic energy loss, thereby reducing the Q value of the resonator and affecting the filter performance.

[0037] To address this issue, this application proposes a method for fabricating a thin-film bulk acoustic resonator, aiming to solve the problem of interface loss caused by abrupt interface changes between the metal electrode and the piezoelectric material. Specifically, in fabricating the thin-film bulk acoustic resonator, a nitriding treatment is first performed on the surface of the bottom electrode 104 to form an interface transition layer 108. For example, after fabricating the molybdenum bottom electrode 104, the surface of the molybdenum bottom electrode 104 is placed in an ammonia atmosphere at a preset pressure range (e.g., 10 mTorr), and heat-treated at a preset target temperature (e.g., 500 °C) and a holding time (e.g., 10 minutes). During this process, nitrogen atoms in the ammonia react with molybdenum atoms on the surface of the molybdenum bottom electrode 104 to form a molybdenum nitride layer with a gradually changing composition. This molybdenum nitride layer, serving as the interface transition layer 108, gradually transitions from pure molybdenum to nitrogen-rich molybdenum nitride, thereby smoothing the material difference between the bottom electrode 104 and the subsequent piezoelectric layer 105 at the atomic scale.

[0038] Subsequently, a piezoelectric layer 105 is fabricated on the interface transition layer 108, and the top electrode 106 of the thin-film bulk acoustic resonator is fabricated on the piezoelectric layer 105. For example, after forming the molybdenum nitride interface transition layer 108, a scandium aluminum nitride (AlScN) piezoelectric layer 105 is deposited on the transition layer using processes such as magnetron sputtering. Due to the presence of the interface transition layer 108, the AlScN piezoelectric layer 105 can better match the surface of the bottom electrode 104 during growth, reducing lattice mismatch and defect generation. Next, the molybdenum top electrode 106 is deposited on the AlScN piezoelectric layer 105.

[0039] Finally, after the top electrode 106 is fabricated, the sacrificial layer 107 in the thin-film bulk acoustic resonator is etched to obtain the thin-film bulk acoustic resonator. For example, if a silicon dioxide sacrificial layer 107 was previously filled on the substrate 101, the silicon dioxide sacrificial layer 107 is removed by wet etching or dry etching after all film layers are fabricated to form the cavity 102 structure required for the resonator.

[0040] Using the above-described preparation method, an in-situ generated composition-gradient interface transition layer 108 is introduced between the bottom electrode 104 and the piezoelectric layer 105. Compared with the conventional method of directly depositing the piezoelectric layer 105 on the bottom electrode 104, the interface transition layer 108 of this application can effectively smooth the abrupt change between the two materials, significantly reducing interface scattering and interface loss. For example, in the conventional method, sound waves encounter a large acoustic impedance mismatch at the interface between the molybdenum electrode and the AlScN piezoelectric layer 105, leading to sound wave energy reflection and loss. In this application, due to the presence of molybdenum nitride (i.e., the interface transition layer 108), the acoustic impedance gradually changes from the molybdenum electrode to the molybdenum nitride and then to the AlScN piezoelectric layer 105, allowing sound waves to pass through the interface more smoothly, thereby significantly suppressing interface loss and improving the Q value of the thin-film bulk acoustic resonator. This technical concept avoids the secondary scattering problem that may be caused by the new interface by eliminating the fundamental cause of the abrupt material interface, rather than introducing an additional independent interface layer, thus providing a reliable acoustic resonance structure for high-performance communication applications.

[0041] In some embodiments, nitriding is performed on the surface of the bottom electrode 104 of the thin-film bulk acoustic resonator to form an interface transition layer 108 on the surface of the bottom electrode 104, including: A radio frequency sputtering process is used to back-sputter nitrogen atoms onto the surface of the bottom electrode 104 to form an interface transition layer 108 on the surface of the bottom electrode 104; or, A nitriding deposition process is used to perform nitriding deposition on the surface of the bottom electrode 104 to form an interface transition layer 108 on the surface of the bottom electrode 104; or, The surface of the bottom electrode 104 is heat-treated with a nitrogen-containing solution to form an interface transition layer 108 on the surface of the bottom electrode 104; or, The surface of the bottom electrode 104 is heat-treated in an ammonia atmosphere to form an interface transition layer 108 on the surface of the bottom electrode 104.

[0042] The use of radio frequency sputtering (RF sputtering) to backsputter the surface of the bottom electrode 104 with nitrogen atoms involves introducing nitrogen gas as a reactant during the RF sputtering process and adjusting process parameters to bombard the surface of the bottom electrode 104 with high-energy nitrogen ions or atoms from the nitrogen plasma. This bombardment causes the metal atoms on the surface of the bottom electrode 104 to react with the active nitrogen, thereby forming a gradually changing interface transition layer 108 in situ on the surface of the bottom electrode 104. This method effectively avoids the introduction of foreign impurities and achieves a smooth transition of interface composition.

[0043] The nitride deposition on the surface of the bottom electrode 104 is performed by plasma-enhanced chemical vapor deposition (PECVD). This means that nitrogen-containing precursor gases (such as ammonia, nitrogen, etc.) and metal precursor gases are introduced through the plasma-enhanced chemical vapor deposition (PECVD) process. Under the action of plasma, these gases react on the surface of the bottom electrode 104 to form a nitride film, which serves as the interface transition layer 108.

[0044] Heat treatment of the bottom electrode 104 surface using a nitrogen-containing solution involves immersing the bottom electrode 104 in a solution containing a nitrogen source and then heating it. The nitrogen source in the solution (e.g., urea, ammonia, nitrate, etc.) decomposes under heat or reacts with the surface of the bottom electrode 104, thereby forming a nitrided layer on the surface of the bottom electrode 104. This nitrided layer serves as an interface transition layer 108. This method is generally simple to operate and has low cost.

[0045] Heat treatment of the bottom electrode 104 surface in an ammonia atmosphere refers to placing the bottom electrode 104 in an environment filled with ammonia (NH3) and heating it. Under high temperature, ammonia decomposes to produce active nitrogen atoms or nitrogen free radicals. These active nitrogen species react with metal atoms on the surface of the bottom electrode 104 to form metal nitrides, thereby forming a nitrided transition layer on the surface of the bottom electrode 104. This nitrided transition layer serves as the interface transition layer 108. In addition to a pure ammonia atmosphere, a mixed atmosphere of ammonia and hydrogen can also be used for heat treatment. Hydrogen can assist in removing surface oxides and improve the nitriding effect. Alternatively, plasma nitriding technology can be used, introducing plasma into the ammonia atmosphere to achieve efficient nitriding at a lower temperature and in a shorter time.

[0046] This application provides various specific process paths for nitriding the surface of the bottom electrode 104 of a thin-film bulk acoustic wave resonator, enabling the formation of a compositionally gradient interface transition layer 108 on the surface of the bottom electrode 104. These nitriding methods, whether based on physical sputtering, chemical vapor deposition, or thermal treatment, all share the core principle of inducing a reaction between the metal atoms of the bottom electrode 104 and an active nitrogen source, thereby constructing a smooth chemical and structural transition region between the metal electrode and the subsequently grown piezoelectric layer 105. This region is the interface transition layer 108. Specifically, in the fabrication method of the thin-film bulk acoustic wave resonator, nitriding is first performed on the surface of the bottom electrode 104 to form the interface transition layer 108. This interface transition layer 108 is not a simple physical stack, but rather, through the aforementioned various nitriding processes, the atomic structure and chemical composition of the bottom electrode 104 surface are altered, forming a continuous gradient region from pure metal to bottom electrode 104 nitride and then to piezoelectric material. This gradual change effectively eliminates the abrupt interface between the metal electrode and the piezoelectric material in traditional processes, thereby significantly reducing the scattering and reflection losses of sound waves at the interface.

[0047] Through these specific nitriding treatments, the scheme of this application ensures that the formed interface transition layer 108 has good uniformity and stability, and that its composition and structure can achieve good matching with the bottom electrode 104 and the piezoelectric layer 105. This not only solves the interface loss problem caused by the abrupt change at the interface between the metal electrode and the piezoelectric material in traditional BAW resonators, but also provides a better substrate for the subsequent growth of the piezoelectric layer 105, further improving the crystal quality and acoustic performance of the piezoelectric layer 105.

[0048] In some embodiments, the surface of the bottom electrode 104 is heat-treated in an ammonia atmosphere to form an interface transition layer 108 on the surface of the bottom electrode 104. This includes placing the surface of the bottom electrode 104 in an ammonia atmosphere within a preset pressure range and heat-treating the surface of the bottom electrode 104 according to a preset target temperature and holding time to form an interface transition layer 108 on the surface of the bottom electrode 104.

[0049] The bottom electrode 104 is placed in an ammonia atmosphere within a preset pressure range, which limits the ammonia pressure within the reaction chamber during the nitriding process. Ammonia, as an active nitrogen source, directly affects the concentration of active nitrogen atoms, the adsorption efficiency on the bottom electrode 104 surface, and the reaction rate with metal atoms. For example, precisely controlling the pressure at 10 mTorr ensures the supply of an appropriate amount of active nitrogen atoms, guaranteeing the effective nitriding reaction while preventing excessively rapid or uneven growth of the nitrided layer due to excessive pressure, thus contributing to a smooth compositional gradient.

[0050] The bottom electrode 104 surface is heat-treated according to a preset target temperature. This feature defines the specific temperature that the bottom electrode 104 surface should reach during the nitriding process. Temperature is a key parameter affecting atomic diffusion rate and chemical reactivity. Setting the target temperature to 500℃ aims to provide sufficient energy to activate the reaction between metal atoms and nitrogen atoms in the bottom electrode 104, promoting nitrogen atom diffusion and nitriding layer formation, while avoiding excessively high temperatures that could lead to abnormal grain growth, structural damage, or material performance degradation in the bottom electrode 104.

[0051] The surface of the bottom electrode 104 is heat-treated according to a preset holding time. This feature limits the duration for which the surface of the bottom electrode 104 needs to maintain the target temperature of 500°C. The holding time directly determines the extent to which nitrogen atoms fully penetrate the surface layer of the bottom electrode 104 and react with metal atoms, as well as the final thickness and compositional gradient of the interface transition layer 108. Setting the holding time to 10 minutes aims to ensure that nitrogen atoms have sufficient time to diffuse and react, forming an interface transition layer 108 with an appropriate thickness and a smooth compositional gradient, while avoiding an excessively thick nitrided layer due to excessive holding time, which could affect the conductivity or overall structural stability of the bottom electrode 104.

[0052] In some embodiments, before nitriding the surface of the bottom electrode 104 of the thin-film bulk acoustic wave resonator, the fabrication method further includes: forming a cavity 102 on the substrate 101 of the thin-film bulk acoustic wave resonator and filling the cavity 102 with a sacrificial layer 107; fabricating a support layer 103 on the substrate 101 and the sacrificial layer 107; and fabricating the bottom electrode 104 of the thin-film bulk acoustic wave resonator on the support layer 103.

[0053] Cavity 102 is a key structure for achieving acoustic resonance in the thin-film bulk acoustic resonator. Its function is to provide an acoustic isolation region, allowing sound waves to be effectively reflected between the piezoelectric layer 105 and the electrodes, thereby forming a standing wave and achieving resonance. The sacrificial layer 107 is the material used to fill cavity 102 during fabrication. Its main function is to maintain the flatness and stability of the structure during subsequent fabrication processes, preventing premature formation of cavity 102 that could lead to collapse or deformation of the upper structure (e.g., support layer 103). After the entire device fabrication is completed, the sacrificial layer 107 is selectively removed, resulting in the final cavity 102 structure, as shown below. Figure 3 As shown. The sacrificial layer 107 can be made of materials such as silicon dioxide, amorphous silicon, or phosphosilicate glass (PSG). These materials typically have good etching selectivity, making them easy to remove without damaging other structures. The support layer 103 is a structure fabricated on top of the substrate 101 and the sacrificial layer 107. Its main function is to provide stable mechanical support for all functional layers subsequently fabricated above, such as the bottom electrode 104, piezoelectric layer 105, and top electrode 106, thereby improving the overall mechanical stability of the structure. Simultaneously, the support layer 103 can also serve as an acoustic reflection layer, helping to reduce energy loss during resonance and thus optimizing the acoustic performance of the resonator.

[0054] This scheme ensures flatness and stability during subsequent structural fabrication by creating a cavity 102 on the substrate 101 and filling it with a sacrificial layer 107, avoiding structural deformation or collapse, and reserving space for the final cavity 102 structure. By fabricating a support layer 103 on the substrate 101 and sacrificial layer 107, stable mechanical support and acoustic optimization are provided for subsequent functional layers. By fabricating a bottom electrode 104 on the support layer 103, the flatness and quality of the bottom electrode 104 are guaranteed, providing a suitable processing object for subsequent nitriding. The clarification and optimization of these preliminary steps allow subsequent nitriding to be performed on a structurally stable and flat bottom electrode 104, thereby ensuring the uniformity and quality of the interface transition layer 108. Ultimately, this effectively suppresses interface losses caused by abrupt interface changes between the metal electrode and the piezoelectric material, significantly improving the Q value and overall performance of the thin-film bulk acoustic resonator.

[0055] In some embodiments, the substrate 101 is made of any one of silicon, sapphire, and silicon carbide.

[0056] In some embodiments, the sacrificial layer 107 is made of at least one of silicon dioxide, amorphous silicon, and phosphosilicate glass; the support layer 103 is made of silicon nitride and / or silicon carbide.

[0057] In some implementations, etching includes either dry etching or liquid wet etching.

[0058] In some embodiments, the top electrode 106 and the bottom electrode 104 are made of at least one of silver, molybdenum, aluminum, niobium and hafnium; the piezoelectric layer 105 is any one of aluminum nitride, aluminum gallium nitride, scandium aluminum nitride and aluminum silicon nitride.

[0059] refer to Figure 2 Secondly, this application provides a thin-film bulk acoustic resonator, comprising: a substrate 101, a support layer 103, a bottom electrode 104, an interface transition layer 108, a piezoelectric layer 105, and a top electrode 106 stacked sequentially; the interface transition layer 108 is a transition layer obtained by nitriding the surface of the bottom electrode 104 of the thin-film bulk acoustic resonator.

[0060] By performing in-situ nitriding on the surface of the bottom electrode 104, the metal atoms of the bottom electrode 104 react chemically with active nitrogen to form an interface transition layer 108 that gradually transitions from pure metal components to nitrides. This smooths the abrupt material interface between the bottom electrode 104 and the piezoelectric layer 105, effectively suppressing the interface scattering phenomenon during sound wave propagation.

[0061] Specifically, the formation process of the interface transition layer 108 utilizes the material of the bottom electrode 104 itself as a reaction source. Under nitriding conditions, the metal atoms on the surface of the bottom electrode 104 combine with nitrogen atoms to form metal nitrides, which constitute the interface transition layer 108. The interior of the interface transition layer 108 exhibits a gradient distribution of metal-nitride composition. For example, when the bottom electrode 104 is made of molybdenum, after heat treatment or plasma treatment in a nitrogen-containing atmosphere, molybdenum atoms react with nitrogen atoms to form molybdenum nitride. Its composition gradually transitions from pure molybdenum at the bottom layer to nitrogen-rich molybdenum nitride at the surface, ultimately achieving continuous acoustic impedance matching with the aluminum nitride or scandium aluminum nitride of the piezoelectric layer 105. This in-situ generated interface transition layer 108 avoids the lattice mismatch and interface defects caused by the direct deposition of the piezoelectric layer 105 in traditional structures, ensuring stable transmission of acoustic wave energy at the interface.

[0062] Through the above technical solution, the reflection coefficient of the sound wave at the interface between the bottom electrode 104 and the piezoelectric layer 105 is significantly reduced, and the interface loss is effectively suppressed. Experimental verification shows that when the bottom electrode 104 (e.g., metallic Mo) is not nitrided (i.e., a conventional resonator), growing a piezoelectric layer 105 (e.g., an AlScN thin film) on the surface of the metallic Mo, and after peeling off the AlScN film, results in a surface roughness of 1.87 nm. Figure 4 As shown, the Q value corresponding to this conventional resonator is 1127, as... Figure 5 As shown; after the bottom electrode 104 (such as metallic Mo) undergoes the nitriding treatment of this application, a piezoelectric layer 105 (such as an AlScN thin film) is grown on the surface of the metallic Mo. After the AlScN thin film is peeled off, the surface roughness of the metallic Mo is significantly reduced to 0.51 nm. Figure 6 As shown, this indicates that nitriding effectively improves interface smoothness and suppresses interface scattering, resulting in a Q value increase of 2832 for the corresponding resonator. Figure 7 As shown, improved interface quality effectively suppresses interface phonon scattering, reduces acoustic energy leakage, and thus improves the Q value and overall performance of the thin-film bulk acoustic resonator. This technical concept avoids secondary scattering problems that might be caused by a new interface by eliminating the fundamental cause of abrupt material interface changes, rather than introducing an additional independent interface layer. This provides a reliable acoustic resonant structure foundation for high-performance communication applications.

[0063] This application provides a filter, including a thin-film bulk acoustic resonator, which is prepared by any of the preparation methods described above.

[0064] The filter described in this application works by integrating a thin-film bulk acoustic wave resonator (BAS) optimized using the aforementioned fabrication method, fundamentally improving the overall performance of the filter. In traditional filters, the abrupt interface change between the metal electrode and the piezoelectric material of the BAS resonator is the main cause of interface loss, which in turn affects key performance indicators such as the filter's Q value and insertion loss. The fabrication method used in this application involves nitriding the surface of the bottom electrode 104 of the BAS resonator to form a compositionally graded in-situ nitrided surface layer, namely the interface transition layer 108. This interface transition layer 108 smoothly transitions the material between the bottom electrode 104 and the piezoelectric layer 105, significantly reducing interface scattering and acoustic energy loss. When this BAS resonator with low interface loss characteristics is applied to a filter, its excellent resonance performance can be directly translated into an overall performance advantage for the filter. Specifically, the improvement of the resonator Q value will enable the filter to have lower insertion loss and steeper out-of-band rejection in the passband, thereby effectively solving the problem of overall performance degradation caused by excessive resonator interface loss in existing filters, and enabling it to meet the stringent requirements of future communication systems for high-performance filters.

[0065] In this document, relational terms such as first and second are used only to distinguish one entity or operation from another entity or operation, without necessarily requiring or implying any such actual relationship or order between these entities or operations.

[0066] The above description is merely an embodiment of this application and is not intended to limit the scope of protection of this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.

Claims

1. A method for fabricating a thin-film bulk acoustic resonator, characterized in that, include: Nitriding is performed on the surface of the bottom electrode (104) of the thin-film bulk acoustic resonator to form an interface transition layer (108) on the surface of the bottom electrode (104). A piezoelectric layer (105) is prepared on the interface transition layer (108), and the top electrode (106) of the thin film bulk acoustic resonator is prepared on the piezoelectric layer (105). After the top electrode (106) is fabricated, the sacrificial layer (107) in the thin-film bulk acoustic resonator is etched to obtain the thin-film bulk acoustic resonator.

2. The method for fabricating a thin-film bulk acoustic resonator according to claim 1, characterized in that, The nitriding treatment on the surface of the bottom electrode (104) of the thin-film bulk acoustic resonator to form an interface transition layer (108) on the surface of the bottom electrode (104) includes: A radio frequency sputtering process is used to back-sputter nitrogen atoms onto the surface of the bottom electrode (104) to form an interface transition layer (108) on the surface of the bottom electrode (104); or, A nitriding deposition process is used to perform nitriding deposition on the surface of the bottom electrode (104) to form an interface transition layer (108) on the surface of the bottom electrode (104); or, The surface of the bottom electrode (104) is heat-treated with a nitrogen-containing solution to form an interface transition layer (108) on the surface of the bottom electrode (104); or, The surface of the bottom electrode (104) is heat-treated in an ammonia atmosphere to form an interface transition layer (108) on the surface of the bottom electrode (104).

3. The method for fabricating a thin-film bulk acoustic resonator according to claim 2, characterized in that, The heat treatment of the surface of the bottom electrode (104) in an ammonia atmosphere to form an interface transition layer (108) on the surface of the bottom electrode (104) includes: The surface of the bottom electrode (104) is placed in an ammonia atmosphere within a preset pressure range, and the surface of the bottom electrode (104) is heat-treated according to a preset target temperature and holding time to form an interface transition layer (108) on the surface of the bottom electrode (104).

4. The method for fabricating a thin-film bulk acoustic resonator according to claim 1, characterized in that, The preparation method further includes, before nitriding the surface of the bottom electrode (104) of the thin-film bulk acoustic resonator: A cavity (102) is provided on the substrate (101) of the thin film bulk acoustic resonator, and a sacrificial layer (107) is filled in the cavity (102). A support layer (103) is prepared on the substrate (101) and the sacrificial layer (107). The bottom electrode (104) of the thin-film bulk acoustic resonator is prepared on the support layer (103).

5. The method for fabricating a thin-film bulk acoustic resonator according to claim 4, characterized in that, The substrate (101) is made of any one of silicon, sapphire, and silicon carbide.

6. The method for fabricating a thin-film bulk acoustic resonator according to claim 4, characterized in that, The material of the sacrificial layer (107) is at least one of silicon dioxide, amorphous silicon, and phosphosilicate glass; The support layer (103) is silicon nitride and / or silicon carbide.

7. The method for fabricating a thin-film bulk acoustic resonator according to claim 4, characterized in that, The etching includes either dry etching or liquid wet etching.

8. The method for fabricating a thin-film bulk acoustic resonator according to claim 1, characterized in that, The materials of the top electrode (106) and the bottom electrode (104) are at least one of silver, molybdenum, aluminum, niobium and hafnium; The piezoelectric layer (105) is any one of aluminum nitride, aluminum gallium nitride, scandium aluminum nitride, and aluminum silicon nitride.

9. A thin-film bulk acoustic resonator, characterized in that, include: The substrate (101), support layer (103), bottom electrode (104), interface transition layer (108), piezoelectric layer (105) and top electrode (106) are stacked in sequence. The interface transition layer (108) is a transition layer obtained by nitriding the surface of the bottom electrode (104) of the thin film bulk acoustic resonator.

10. A filter, characterized in that, include: A thin-film bulk acoustic resonator, wherein the thin-film bulk acoustic resonator is prepared by the preparation method described in any one of claims 1-8.

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