A filter and a method of manufacturing the same

Abstract

The application belongs to the technical field of filters, and discloses a filter and a preparation method thereof. The filter comprises, from bottom to top, a composite substrate, a lower electrode layer, a piezoelectric layer, an upper electrode layer and a dielectric layer which are stacked in sequence. The composite substrate comprises, from bottom to top, a substrate layer, a trap-rich layer and a support layer which are stacked in sequence. The trap-rich layer is used for improving the acoustic insulation performance of the composite substrate. The dielectric layer fully covers the upper surface of the filter. The dielectric layer is used for inhibiting the acoustic energy leakage of the filter and maintaining the stable performance of the filter under high-temperature and high-humidity conditions. The filter has mechanical stability and long-term reliability.

Description

Technical Field

[0001] This application relates to the field of filter technology, and more specifically, to a filter and its fabrication method. Background Technology

[0002] With the rapid development of mobile communication technology, radio frequency (RF) front-end devices face urgent demands for higher frequencies, smaller sizes, and wider bandwidth. As a core component of the RF front-end, the performance of acoustic wave filters directly affects the overall quality of the communication system. Currently, acoustic resonators are mainly divided into two categories: surface acoustic wave (SAW) devices and bulk acoustic wave (BAW) devices. Among them, thin-film bulk acoustic resonators (FBARs) have become a research hotspot in the 5G communication field due to their advantages such as small size, low insertion loss, and high quality factor. A typical FBAR device adopts a sandwich stack structure consisting of a bottom electrode, a piezoelectric layer, and a top electrode, achieving the mutual conversion between electrical signals and mechanical resonance through the piezoelectric effect.

[0003] However, existing FBAR technology still has many shortcomings. For example, when the resonators are too close together, acoustic waves are prone to leakage and coupling through the substrate, resulting in prominent out-of-band spurious phenomena and poor isolation, thus affecting the acoustic insulation performance of the filter. In addition, the stiffness of piezoelectric and electrode materials decreases with increasing temperature, leading to a decrease in sound velocity and frequency drift, which seriously affects the performance stability of the device in high-temperature and high-humidity environments. Existing solutions mostly adopt a bottom-up fabrication approach, which can achieve basic functions, but still has significant shortcomings in substrate acoustic insulation, temperature drift suppression, and acoustic wave energy confinement, requiring further optimization.

[0004] To address the aforementioned issues, existing technologies urgently need improvement. Summary of the Invention

[0005] The purpose of this application is to provide a filter and its fabrication method. By introducing a trap-rich layer to improve the acoustic insulation performance of the composite substrate and a dielectric layer that fully covers the upper surface of the filter, the shortcomings of existing acoustic filters in terms of acoustic insulation performance, high temperature and humidity stability, and acoustic energy leakage suppression are solved. By introducing a trap-rich layer and a fully covered dielectric layer, the acoustic insulation performance of the composite substrate can be improved while effectively protecting the performance stability of the filter under high temperature and humidity conditions, thereby improving the reliability of the filter.

[0006] In a first aspect, this application provides a filter comprising a composite substrate, a lower electrode layer, a piezoelectric layer, an upper electrode layer, and a dielectric layer stacked sequentially from bottom to top; The composite substrate comprises a substrate layer, a trap-rich layer, and a support layer stacked sequentially from bottom to top; The trap-rich layer is used to improve the acoustic insulation properties of the composite substrate; The dielectric layer fully covers the upper surface of the filter. The dielectric layer is used to suppress the leakage of acoustic energy of the filter and maintain the stable performance of the filter under high temperature and high humidity conditions.

[0007] The filter provided in this application addresses the shortcomings of existing acoustic filters in terms of acoustic insulation performance, high temperature and humidity stability, and acoustic energy leakage suppression by introducing a trap-rich layer to improve the acoustic insulation performance of the composite substrate and a dielectric layer that fully covers the upper surface of the filter. By introducing the trap-rich layer and the fully covered dielectric layer, the filter's performance stability under high temperature and humidity conditions can be effectively protected while improving the acoustic insulation performance of the composite substrate, thereby improving the reliability of the filter.

[0008] Optionally, the composite substrate has a groove inside; the groove is located in the support layer, so that a cavity structure is formed between the trap-rich layer and the lower electrode layer.

[0009] The filter provided in this application, by setting grooves and forming a cavity structure inside the composite substrate, can further optimize the sound wave propagation path, enhance the acoustic insulation effect, and effectively suppress the leakage and coupling of sound waves in the substrate, thereby improving the out-of-band suppression capability and isolation of the filter.

[0010] Optionally, the substrate layer is made of at least one of monocrystalline silicon, polycrystalline silicon, sapphire, spinel, lithium tantalate, lithium niobate, lithium gallium oxide, zinc oxide, and zirconium oxide ceramic.

[0011] Optionally, the material of the trap-rich layer is at least one of silicon oxide, silicon nitride, and silicon oxynitride.

[0012] Optionally, the support layer is made of at least one of monocrystalline silicon, polycrystalline silicon, sapphire, spinel, lithium tantalate, lithium niobate, lithium gallium oxide, zinc oxide, and zirconium oxide ceramic.

[0013] Optionally, the material of the lower electrode layer is at least one of copper, gold, silver, chromium, platinum, aluminum, molybdenum, tungsten, titanium, and ruthenium.

[0014] Optionally, the piezoelectric layer is made of at least one of monocrystalline aluminum nitride, polycrystalline aluminum nitride, zinc oxide, lead zirconate titanate, lithium niobate, lithium tantalate, and polyvinylidene fluoride.

[0015] Optionally, the upper electrode layer is made of at least one of copper, gold, silver, chromium, platinum, aluminum, molybdenum, tungsten, titanium, and ruthenium.

[0016] Optionally, the dielectric layer is made of at least one of silicon oxide, silicon nitride, and silicon oxynitride.

[0017] Secondly, this application provides a method for fabricating a filter, used to fabricate the filter as described above, comprising: After forming a trap-rich layer on the substrate, the trap-rich layer is bonded to the support layer at low temperature to obtain the first composite substrate. Groove etching is performed on the support layer on the surface of the first composite substrate to obtain a second composite substrate with a cavity structure; A lower electrode layer, a piezoelectric layer, and an upper electrode layer are sequentially deposited on the second composite substrate to obtain an initial filter with a stacked structure. A dielectric layer covering the entire surface of the initial filter is deposited to obtain the filter.

[0018] The filter fabrication method provided in this application can realize the fabrication of filters. Through processes such as low-temperature bonding, groove etching, and layer deposition, the structure of each layer can be precisely controlled, effectively forming filters with excellent acoustic insulation performance and environmental stability, providing a reliable process basis for mass production.

[0019] Beneficial effects: The filter and its fabrication method provided in this application solve the problems of existing acoustic wave filters in terms of acoustic insulation performance, high temperature and high humidity stability, and acoustic energy leakage suppression by introducing a trap-rich layer to improve the acoustic insulation performance of the composite substrate and a dielectric layer that fully covers the upper surface of the filter. By introducing a trap-rich layer and a fully covered dielectric layer, the acoustic insulation performance of the composite substrate can be improved while effectively protecting the performance stability of the filter under high temperature and high humidity conditions, thereby improving the reliability of the filter. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the filter structure provided in an embodiment of this application.

[0021] Figure 2 This is a schematic flowchart illustrating the filter fabrication method provided in an embodiment of this application.

[0022] Labeling explanations: 1. Composite substrate; 2. Lower electrode layer; 3. Piezoelectric layer; 4. Upper electrode layer; 5. Dielectric layer; 6. Substrate layer; 7. Trap-rich layer; 8. Support layer; 9. Cavity structure. Detailed Implementation

[0023] 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.

[0024] 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.

[0025] Please refer to Figure 1 , Figure 1 This is a filter in some embodiments of the present application, comprising a composite substrate 1, a lower electrode layer 2, a piezoelectric layer 3, an upper electrode layer 4, and a dielectric layer 5 stacked from bottom to top; The composite substrate 1 includes a substrate layer 6, a trap-rich layer 7, and a support layer 8 stacked sequentially from bottom to top; The trap-rich layer 7 is used to improve the acoustic insulation properties of the composite substrate 1; Dielectric layer 5 covers the upper surface of the filter. Dielectric layer 5 is used to suppress acoustic energy leakage of the filter and maintain the filter's performance stability under high temperature and high humidity conditions.

[0026] In practical applications, this filter significantly improves its acoustic insulation performance and environmental stability by introducing a trap-rich layer 7 and a dielectric layer 5.

[0027] The composite substrate 1 is the basic supporting structure of the entire filter, comprising a substrate layer 6, a trap-rich layer 7, and a support layer 8. The substrate layer 6, serving as the base of the entire composite substrate 1, provides mechanical support and is made of at least one of the following materials: monocrystalline silicon, polycrystalline silicon, sapphire, spinel, lithium tantalate, lithium niobate, lithium gallium oxide, zinc oxide, and zirconium oxide ceramic. The trap-rich layer 7 is a material layer capable of effectively "capturing" or "absorbing" acoustic wave energy, crucial for improving acoustic insulation performance. It can be designed with materials possessing specific acoustic impedance characteristics; for example, it can employ a porous structure or materials with acoustic absorption capabilities, such as at least one of silicon oxide, silicon nitride, and silicon oxynitride, to effectively absorb and scatter acoustic wave energy, thereby improving the acoustic insulation performance of the composite substrate 1. The support layer 8 further enhances the overall structural strength and stability of the composite substrate 1 and is made of at least one of the following materials: monocrystalline silicon, polycrystalline silicon, sapphire, spinel, lithium tantalate, lithium niobate, lithium gallium oxide, zinc oxide, and zirconium oxide ceramic.

[0028] The lower electrode layer 2 and the upper electrode layer 4 are key components for converting electrical signals into mechanical resonance. The lower electrode layer 2 can be deposited on top of the composite substrate 1 using methods such as sputtering, evaporation, or electroplating. The material of the lower electrode layer 2 is at least one of copper, gold, silver, chromium, platinum, aluminum, molybdenum, tungsten, titanium, and ruthenium. The upper electrode layer 4 can be deposited on top of the piezoelectric layer 3 using a similar method to the lower electrode layer 2. The material of the upper electrode layer 4 is at least one of copper, gold, silver, chromium, platinum, aluminum, molybdenum, tungsten, titanium, and ruthenium.

[0029] The piezoelectric layer 3 is the core functional layer for realizing electroacoustic conversion. The piezoelectric layer 3 can be grown above the lower electrode layer 2 using thin film deposition techniques, such as magnetron sputtering, pulsed laser deposition, or atomic layer deposition. Its material is at least one of single-crystal aluminum nitride, polycrystalline aluminum nitride, zinc oxide, lead zirconate titanate, lithium niobate, lithium tantalate, and polyvinylidene fluoride.

[0030] The dielectric layer 5 covers the top layer of the filter. Its main function is to further suppress the leakage of acoustic energy to the external environment and provide a protective barrier for the filter so that it can maintain stable performance when facing harsh environments such as high temperature and high humidity. Its material is at least one of silicon oxide, silicon nitride, and silicon oxynitride.

[0031] This filter addresses the shortcomings of existing acoustic filters in terms of acoustic insulation performance, high-temperature and high-humidity stability, and acoustic energy leakage suppression by introducing a trap-rich layer to improve the acoustic insulation performance of the composite substrate and a dielectric layer that fully covers the upper surface of the filter. By introducing a trap-rich layer and a fully covered dielectric layer, the filter's performance stability under high-temperature and high-humidity conditions can be effectively protected while improving the acoustic insulation performance of the composite substrate, thus improving the reliability of the filter.

[0032] Specifically, a groove is provided inside the composite substrate 1; the groove is located in the support layer 8, so that a cavity structure 9 is formed between the trap-rich layer 7 and the lower electrode layer 2.

[0033] In practical applications, a groove refers to one or more unfilled regions formed within the support layer 8 of the composite substrate 1. The shape of the groove can be adjusted according to actual design requirements, such as being circular, elliptical, rectangular, or other irregular shapes. The depth and width of the groove can also be optimized according to the desired acoustic characteristics. The groove arrangement allows for the removal or thinning of specific areas of the support layer 8, thereby forming a cavity structure 9 below the trap-rich layer 7 and above the lower electrode layer 2. This cavity structure 9 is a gas- or vacuum-filled gap between the trap-rich layer 7 and the lower electrode layer 2. In practical applications, this cavity structure can be achieved by etching processes on the support layer 8, such as wet etching, dry etching, or plasma etching. The cavity structure 9 can alter the propagation path and medium of acoustic waves within the composite substrate 1, thereby affecting the resonant characteristics and acoustic isolation effect of the filter.

[0034] Specifically, when sound waves propagate downwards from the piezoelectric layer 3, they encounter the cavity structure 9. Due to the significant difference in acoustic impedance between the internal medium (such as air or vacuum) and the surrounding solid materials (such as the trap-rich layer 7 and the support layer 8), the sound waves undergo strong reflection and refraction at the interface. This acoustic impedance mismatch effect confines most of the sound wave energy within the piezoelectric layer 3 and the structure above it, making it difficult for it to leak downwards to the rest of the composite substrate 1. Furthermore, the cavity structure 9 acts as an acoustic trap, further suppressing unwanted sound wave modes and reducing the transfer of sound wave energy to the substrate layer 6, thereby reducing substrate loss. It is precisely the presence of the cavity structure 9 that further enhances the acoustic insulation performance of the trap-rich layer 7, effectively isolating the coupling between the sound waves generated by the piezoelectric layer 3 and the underlying substrate layer 6, thus reducing the leakage of sound wave energy.

[0035] As can be seen from the above, this filter, by introducing a trap-rich layer to improve the acoustic insulation performance of the composite substrate and a dielectric layer that fully covers the upper surface of the filter, solves the problems of existing acoustic filters in terms of acoustic insulation performance, high temperature and humidity stability, and acoustic energy leakage suppression. By introducing a trap-rich layer and a fully covered dielectric layer, the filter can effectively protect its performance stability under high temperature and humidity conditions while improving the acoustic insulation performance of the composite substrate, thus improving the reliability of the filter.

[0036] Please refer to Figure 2 , Figure 2 This is a method for fabricating a filter according to some embodiments of this application, used to fabricate the filter as described above, comprising: Step S1: After forming a trap-rich layer on the substrate, the trap-rich layer is bonded to the support layer at low temperature to obtain the first composite substrate. Step S2: Groove etching is performed on the support layer on the surface of the first composite substrate to obtain a second composite substrate with a cavity structure. Step S3: Sequentially deposit a lower electrode layer, a piezoelectric layer, and an upper electrode layer on the second composite substrate to obtain an initial filter with a stacked structure; Step S4: Deposit a fully covered dielectric layer on the upper surface of the initial filter to obtain the filter.

[0037] The filter fabrication method provided in this application can realize the fabrication of filters. Through processes such as low-temperature bonding, groove etching, and layered deposition, the structure of each layer can be precisely controlled, effectively forming filters with excellent acoustic insulation performance and environmental stability, providing a reliable process basis for mass production.

[0038] Specifically, in step S1, after forming a trap-rich layer 7 on the substrate layer 6, the trap-rich layer 7 is low-temperature bonded to the support layer 8 to obtain the first composite substrate. The substrate layer 6 serves as the initial substrate, and its material can be selected according to actual needs, such as monocrystalline silicon, polycrystalline silicon, or sapphire. The formation of the trap-rich layer 7 can be achieved through various thin-film deposition techniques, such as chemical vapor deposition (CVD), physical vapor deposition (PVD), or spin coating, to form a material with specific acoustic absorption or scattering characteristics on the substrate layer 6. Subsequently, the substrate layer 6 with the formed trap-rich layer 7 is low-temperature bonded to the support layer 8. Low-temperature bonding techniques can employ methods such as plasma-activated bonding, surface-activated bonding, or eutectic bonding, the purpose of which is to achieve a tight bond between the two layers at a lower temperature, avoiding the adverse effects of high temperatures on material properties and ensuring the structural integrity and stability of the composite substrate. Thus, a first composite substrate with good acoustic insulation potential is formed.

[0039] Specifically, in step S2, groove etching is performed on the support layer 8 on the surface of the first composite substrate to obtain a second composite substrate with a cavity structure. This etching step is crucial for forming the cavity structure inside the filter. The etching process can employ wet etching or dry etching techniques (such as reactive ion etching (RIE) or deep reactive ion etching (DRIE). By precisely controlling the etching depth and shape, one or more grooves can be formed in the support layer 8, creating a cavity structure between the trap-rich layer 7 and the subsequently deposited lower electrode layer 2. This cavity structure effectively isolates the propagation of acoustic waves in the substrate, further enhancing the acoustic insulation performance of the filter.

[0040] Specifically, in step S3, a lower electrode layer 2, a piezoelectric layer 3, and an upper electrode layer 4 are sequentially deposited on the second composite substrate to obtain an initial filter with a stacked structure. The deposition of the lower electrode layer 2 can employ techniques such as sputtering, evaporation, or electroplating to ensure tight bonding with the second composite substrate and good conductivity. Subsequently, the piezoelectric layer 3 is deposited on top of the lower electrode layer 2. The piezoelectric layer 3 is the core functional layer for electroacoustic conversion, and its deposition can employ thin film growth techniques such as magnetron sputtering, pulsed laser deposition, or atomic layer deposition to obtain a high-quality piezoelectric thin film. Finally, the upper electrode layer 4 is deposited on top of the piezoelectric layer 3, with a deposition method similar to that of the lower electrode layer 2. Through these sequential deposition steps, the core electrode-piezoelectric-electrode sandwich structure of the filter is formed.

[0041] Specifically, in step S4, a dielectric layer 5 is deposited on the upper surface of the initial filter to form a fully covered filter. The dielectric layer 5 can be deposited using methods such as chemical vapor deposition (CVD), physical vapor deposition (PVD), or spin coating to ensure it fully covers the upper surface of the entire stacked structure. The introduction of the dielectric layer 5 not only further suppresses the leakage of acoustic energy to the external environment, but more importantly, it provides an effective protective barrier for the filter, enabling it to maintain stable performance under harsh environments such as high temperature and high humidity, and effectively reducing frequency drift.

[0042] As can be seen from the above, the fabrication method of this filter involves forming a trap-rich layer on a substrate, then bonding the trap-rich layer to a support layer at low temperature to obtain a first composite substrate. The support layer on the surface of the first composite substrate is then etched with grooves to obtain a second composite substrate with a cavity structure. A lower electrode layer, a piezoelectric layer, and an upper electrode layer are then deposited sequentially on top of the second composite substrate to obtain an initial filter with a stacked structure. Finally, a fully covered dielectric layer is deposited on the upper surface of the initial filter to obtain the filter. Thus, through processes such as low-temperature bonding, groove etching, and layered deposition, the structure of each layer can be precisely controlled, effectively forming a filter with excellent acoustic insulation performance and environmental stability, providing a reliable technological foundation for mass production.

[0043] 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.

[0044] 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 filter, characterized in that, It includes a composite substrate (1), a lower electrode layer (2), a piezoelectric layer (3), an upper electrode layer (4), and a dielectric layer (5) stacked from bottom to top. The composite substrate (1) includes a substrate layer (6), a trap-rich layer (7) and a support layer (8) stacked sequentially from bottom to top. The trap-rich layer (7) is used to improve the acoustic insulation properties of the composite substrate (1); The dielectric layer (5) fully covers the upper surface of the filter. The dielectric layer (5) is used to suppress the acoustic energy leakage of the filter and maintain the performance stability of the filter under high temperature and high humidity conditions.

2. The filter according to claim 1, characterized in that, The composite substrate (1) has a groove inside; the groove is located in the support layer (8), so that a cavity structure (9) is formed between the trap-rich layer (7) and the lower electrode layer (2).

3. The filter according to claim 1, characterized in that, The substrate layer (6) is made of at least one of the following materials: monocrystalline silicon, polycrystalline silicon, sapphire, spinel, lithium tantalate, lithium niobate, lithium gallium oxide, zinc oxide, and zirconium oxide ceramic.

4. The filter according to claim 1, characterized in that, The trap-rich layer (7) is made of at least one of silicon oxide, silicon nitride, and silicon oxynitride.

5. The filter according to claim 1, characterized in that, The material of the support layer (8) is at least one of monocrystalline silicon, polycrystalline silicon, sapphire, spinel, lithium tantalate, lithium niobate, lithium gallium oxide, zinc oxide, and zirconium oxide ceramic.

6. The filter according to claim 1, characterized in that, The material of the lower electrode layer (2) is at least one of copper, gold, silver, chromium, platinum, aluminum, molybdenum, tungsten, titanium, and ruthenium.

7. The filter according to claim 1, characterized in that, The piezoelectric layer (3) is made of at least one of monocrystalline aluminum nitride, polycrystalline aluminum nitride, zinc oxide, lead zirconate titanate, lithium niobate, lithium tantalate, and polyvinylidene fluoride.

8. The filter according to claim 1, characterized in that, The material of the upper electrode layer (4) is at least one of copper, gold, silver, chromium, platinum, aluminum, molybdenum, tungsten, titanium, and ruthenium.

9. The filter according to claim 1, characterized in that, The dielectric layer (5) is made of at least one of silicon oxide, silicon nitride, and silicon oxynitride.

10. A method for fabricating a filter, characterized in that, For fabricating the filter as described in any one of claims 1 to 9, comprising: After forming a trap-rich layer on the substrate, the trap-rich layer is bonded to the support layer at low temperature to obtain the first composite substrate. Groove etching is performed on the support layer on the surface of the first composite substrate to obtain a second composite substrate with a cavity structure; A lower electrode layer, a piezoelectric layer, and an upper electrode layer are sequentially deposited on the second composite substrate to obtain an initial filter with a stacked structure. A dielectric layer covering the entire surface of the initial filter is deposited to obtain the filter.

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