Electromagnetic MEMS loudspeaker and manufacturing method thereof

Abstract

The application relates to the technical field of loudspeakers, in particular to an electromagnetic MEMS loudspeaker and a preparation method thereof. The electromagnetic MEMS loudspeaker does not contain any permanent magnet, can generate a magnetic field, is free from the dependence on the permanent magnet, is compact in structure, small in size and easy to integrate with equipment. Moreover, the electromagnetic MEMS loudspeaker has a multilayer coil structure, reduces impedance, realizes low-voltage direct drive and improves sound pressure level output. The loudspeaker comprises a plurality of coil assemblies and a vibrating diaphragm which are arranged in a stacking mode along a first direction, and an insulating layer is arranged between the plurality of coil assemblies, wherein each coil assembly comprises a coil and a soft magnetic core, the coil is arranged around the outer periphery of the soft magnetic core, the plurality of coil assemblies are arranged in parallel, and the first direction is perpendicular to the vibrating diaphragm.

Description

Technical Field

[0001] This application relates to the field of loudspeaker technology, and in particular to an electromagnetic MEMS loudspeaker and its fabrication method. Background Technology

[0002] MEMS loudspeakers, due to their small size, low power consumption, and compatibility with integrated circuit processes, have become an ideal choice for audio units in portable electronic devices such as true wireless earbuds, hearing aids, and smart glasses. To obtain sufficient driving force, existing electromagnetic MEMS loudspeaker coil structures often increase the coil length. However, this significantly increases the total resistance, limiting the current under low-voltage driving, thus preventing an effective increase in the Lorentz force. Summary of the Invention

[0003] To address the aforementioned issues, this application provides an electromagnetic MEMS loudspeaker and its fabrication method. This electromagnetic MEMS loudspeaker contains no permanent magnets, generates its own magnetic field, and eliminates dependence on permanent magnets, resulting in a compact structure, small size, and ease of device integration. Furthermore, its multi-layered coil structure reduces impedance, enables low-voltage direct drive, and improves sound pressure level output.

[0004] The electromagnetic MEMS loudspeaker provided in the embodiments of this application includes a plurality of coil assemblies and a diaphragm stacked along a first direction, with an insulating layer between the plurality of coil assemblies, wherein each coil assembly includes a coil and a soft magnetic core, the coil being wound around the outer periphery of the soft magnetic core; the plurality of coil assemblies are arranged in parallel, and the first direction is perpendicular to the diaphragm.

[0005] In the above embodiments, the parallel structure of the multi-layer coil assembly achieves high sound pressure level under low voltage. Compared with single-layer or series-connected multi-layer coils, the multiple parallel coil assemblies of this application can effectively increase the total length of the coil without increasing the total resistance. This allows the speaker of this application to obtain a larger driving current under the 1Vrms standard audio signal of a mobile phone, thereby multiplying the Lorentz force and achieving high sound pressure level output, with a target of 110dB SPL, which is suitable for application scenarios such as "direct drive from 3.5mm headphone jack". Moreover, this speaker does not contain any permanent magnets and can generate its own magnetic field, eliminating the dependence on permanent magnets and making the structure compact, small in size, and easy to integrate into devices.

[0006] In one embodiment, the vertical projections of the plurality of coil assemblies along the first direction completely overlap.

[0007] In one embodiment, the coil includes a first part and a second part, both of which are bow-shaped coiled structures, and the first part and the second part are symmetrically arranged on both sides of the soft magnetic core.

[0008] In one embodiment, the number n of the coil assemblies satisfies: 2≤n≤5.

[0009] In one embodiment, the loudspeaker further includes a housing and a mounting frame, the mounting frame being mounted at an opening in the housing, and the diaphragm being mounted on the mounting frame.

[0010] In one embodiment, the loudspeaker further includes a circuit board, which is arranged along the first direction with the diaphragm and spaced at a predetermined distance from the diaphragm, and the plurality of coil assemblies are electrically connected to the circuit board.

[0011] In one embodiment, the coil includes a first electrode and a second electrode, and the electromagnetic MEMS loudspeaker further includes a first conductive post and a second conductive post, the first electrode being connected to the first conductive post and the second electrode being connected to the second conductive post; the first conductive post and the second conductive post are respectively connected to the circuit board and both extend along the first direction, and the diaphragm and the insulating film both have clearance holes through which the first conductive post and the second conductive post pass.

[0012] In one embodiment, the vibrating membrane is a single-crystal silicon or silicon nitride thin film, and the thickness 'a' of the vibrating membrane satisfies: 1.0 μm ≤ a ≤ 2.0 μm.

[0013] In one embodiment, the coil is made of a copper-nickel nanocomposite material, wherein nickel is uniformly dispersed in the form of nanoparticles in a copper matrix.

[0014] In one embodiment, the nickel nanoparticles have a particle size of 25 nm to 50 nm.

[0015] In one embodiment, the linewidth of the coil is b, which satisfies: 5μm≤b≤15μm.

[0016] In one embodiment, the insulating layer is a silicon oxide or silicon nitride film, and the thickness of the insulating layer is c, which satisfies: 0.5μm≤c≤1.5μm.

[0017] The embodiments of this application also provide a method for fabricating the above-mentioned electromagnetic MEMS loudspeaker, comprising the following steps: S1: A substrate is provided, on which a seed layer and a sacrificial layer are sequentially prepared, and a pattern of a coil assembly is defined on the sacrificial layer by photolithography; the substrate is a vibrating diaphragm. S2: The coil assembly is formed within the pattern of the coil assembly using an electroplating process; S3: Remove the sacrificial layer and the uncovered seed layer; S4: Deposited insulating layer; S5: A seed layer and a sacrificial layer are sequentially prepared on the insulating layer, and the pattern of the coil assembly is defined on the sacrificial layer by photolithography. S6: Repeat steps S2 to S5 according to the preset number of sub-coil layers.

[0018] In one embodiment, step S2: forming a coil assembly within a pattern using an electroplating process includes: depositing an alkaline cyanide-free copper plating solution within the coil pattern of the coil assembly, and continuously stirring the alkaline cyanide-free copper plating solution, wherein the alkaline cyanide-free copper plating solution contains nickel nanoparticles with a particle size of 25nm to 50nm and a concentration of 1.5g / L to 2.5g / L. Attached Figure Description

[0019] Figure 1 An exploded view of an electromagnetic MEMS loudspeaker provided for one embodiment of this application; Figure 2 Another exploded view of an electromagnetic MEMS loudspeaker from one embodiment of this application; Figure 3 A structural diagram of a coil assembly provided in one embodiment of this application; Figure 4 This is a partial enlarged view of a coil assembly provided in one embodiment of this application.

[0020] Figure label: 1-Vibrating diaphragm; 2-Insulating layer; 31-Coil; 311-First electrode; 312-Second electrode; 32-Soft magnetic core; A-First part; B-Second part; 4-Housing; 5-Mounting frame; 6-Circuit board; 7-First conductive post; 8-Second conductive post. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description of the application is provided in conjunction with the accompanying drawings and embodiments.

[0022] The terminology used in the following embodiments is for the purpose of describing particular embodiments only and is not intended to be limiting of this application. As used in the specification and appended claims of this application, the singular expressions “a,” “an,” “the,” “the,” “the,” and “this” are intended to also include expressions such as “one or more” unless the context clearly indicates otherwise.

[0023] References to “an embodiment” or “a specific embodiment” as used in this specification mean that one or more embodiments of this application include a particular feature, structure, or characteristic described in connection with that embodiment. The terms “comprising,” “including,” “having,” and variations thereof mean “including, but not limited to,” unless otherwise specifically emphasized.

[0024] MEMS (Micro-Electro-Mechanical Systems) loudspeakers are miniature electroacoustic transducers integrated on silicon chips using semiconductor micro-nano manufacturing processes based on micro-electro-mechanical systems technology. They can directly convert electrical signals into sound waves. Currently, mainstream MEMS loudspeakers are mainly divided into two categories: piezoelectric and electrostatic. Piezoelectric MEMS loudspeakers utilize the inverse piezoelectric effect of piezoelectric materials to drive a diaphragm to produce sound, but their high-frequency response is often limited, and their materials and processes are complex. Electrostatic MEMS loudspeakers require a higher DC bias voltage and typically necessitate an external or internal charge pump, increasing the difficulty of system integration and power consumption.

[0025] Compared to piezoelectric and electrostatic MEMS speakers, electromagnetic MEMS speakers offer systemic advantages in power density, driving voltage, linear response, and mass production compatibility, making them the mainstream technology in current consumer electronics (such as mobile phones and TWS earphones). The principle of electromagnetic MEMS speakers is based on the Lorentz force: a micro-coil is placed in a magnetic field provided by a permanent magnet; when the coil is energized, the force drives the diaphragm to vibrate. However, in related technologies, electromagnetic MEMS speakers must rely on external permanent magnets, such as neodymium iron boron magnets, to provide a constant operating magnetic field. This increases the overall size and assembly complexity of the device. Furthermore, integrating the permanent magnet, whether as a separate component or through sputtering, increases processing costs and poses challenges to the compatibility of MEMS back-end processes.

[0026] Furthermore, to obtain sufficient driving force within a limited chip area, it is usually necessary to increase the number of turns or the length of the coil. However, the area of ​​a single-layer coil is limited, and while a multi-layer coil using a simple interlayer series design increases the coil length, it also significantly increases the coil resistance. Under low voltage (such as an audio signal of 1Vrms), the current is limited, resulting in the Lorentz force not being effectively increased.

[0027] In view of this, embodiments of this application provide an electromagnetic MEMS loudspeaker and a method for fabricating the same. This electromagnetic MEMS loudspeaker does not contain any permanent magnets, is capable of generating its own magnetic field, and is free from dependence on permanent magnets, resulting in a compact structure, small size, and easy device integration. Furthermore, it has a multi-layer coil structure, which reduces impedance, enables low-voltage direct drive, and improves sound pressure level output.

[0028] The embodiments of this application will now be described in detail with reference to the accompanying drawings.

[0029] like Figures 1-4 As shown, an embodiment of this application provides an electromagnetic MEMS loudspeaker, which includes a plurality of coil assemblies and a diaphragm 1 stacked along a first direction perpendicular to the diaphragm 1. An insulating layer 2 is provided between the plurality of coil assemblies to prevent short circuits caused by contact between the coil assemblies in each layer. Each coil assembly includes a coil 31 and a soft magnetic core 32, with the coil 31 wound around the outer periphery of the soft magnetic core 32. The plurality of coil assemblies are electrically connected in parallel to each other and are connected to the diaphragm 1.

[0030] The electromagnetic MEMS speaker of this application can be applied to portable and wearable devices such as mobile phones, headphones, and watches. In the above embodiments, the parallel structure of the multi-layer coil assembly achieves high sound pressure level at low voltage. Compared with single-layer or series-connected multi-layer coils, the multiple parallel coil assemblies of this application can effectively increase the total length of the coil 31 without increasing the total resistance. This allows the speaker of this application to obtain a larger driving current under the 1Vrms standard audio signal of a mobile phone, thereby multiplying the Lorentz force and achieving high sound pressure level output, with a target of 110dB SPL, which is suitable for application scenarios such as "direct drive from 3.5mm headphone jack". The speaker does not contain any permanent magnets and can generate its own magnetic field, eliminating the dependence on permanent magnets, making the structure compact, small in size, and easy to integrate into devices.

[0031] In one embodiment, the vertical projections of a plurality of coil assemblies along a first direction completely overlap. "Complete overlap" as described above refers to overlap within an acceptable error range, with deviations controlled within ±3 μm.

[0032] In one embodiment, the coil 31 is a planar coil. The coil 31 includes a first part A and a second part B, both of which are bow-shaped coiled structures and symmetrically arranged on both sides of the soft magnetic core 32. It is worth noting that the first part A and the second part B of the coil 31 are an integral structure, formed by bending and coiling a single wire. This allows for a longer coil length, enabling a larger driving current and thus increasing the Lorentz force.

[0033] In another embodiment, the coil 31 can also be a planar helical coil with a line width of about 10 μm, a line spacing of about 10 μm, and 20 turns.

[0034] In one embodiment, the number n of the coil components satisfies: 2 ≤ n ≤ 5. For example, the number of coil components can specifically be 2, 3, 4, or 5. Of course, the number of coil components can also be other, and can be set according to requirements; this application does not impose specific limitations.

[0035] In one embodiment, the soft magnetic core 32 is made of 1J85 iron-nickel-molybdenum soft magnetic alloy, prepared by a combined magnetron sputtering and electroplating process, with a thickness of 4 μm. Its composition is: Ni 80.2%, Mo 5.0%, and Fe balance. This soft magnetic layer undergoes vacuum annealing at 400℃, achieving an initial permeability μi of 35000.

[0036] In one embodiment, the electromagnetic MEMS loudspeaker further includes a housing 4 and a mounting frame 5, the housing 4 having a receiving cavity. The housing 4 can be rectangular, with an opening at one end, and the mounting frame 5 is mounted at the opening of the housing 4. The depth of the receiving cavity is approximately 200-300 μm, providing space for the vibration of the diaphragm 1. The mounting frame 5 is a rectangular frame, with the same length and width as the housing 4, and the diaphragm 1 is mounted within the mounting frame 5 so that the diaphragm 1 is suspended on one side of the receiving cavity of the housing 4. Both the housing 4 and the mounting frame 5 are made of monocrystalline silicon. The housing 4 is provided with a sound outlet.

[0037] In one embodiment, the electromagnetic MEMS loudspeaker further includes a circuit board 6, which is arranged along the back of the diaphragm 1 in a first direction. A coil assembly is electrically connected to the circuit board 6, and the diaphragm 1 is spaced apart from the circuit board 6 by a predetermined distance. Specifically, the mounting frame 5 has a certain thickness, the thickness direction of which is the first direction. The mounting frame 5 is located between the housing 4 and the circuit board 6, and the diaphragm 1 is mounted within the mounting frame 5, creating a gap between the diaphragm 1 and the circuit board 6.

[0038] In one embodiment, the coil 31 includes a first electrode 311 and a second electrode 312. The coil 31 is formed by bending and coiling a single, continuous wire. The two ends of the wire can extend outwards from the coil 31 as the first electrode 311 and the second electrode 312. The speaker also includes a first conductive post 7 and a second conductive post 8, with the first electrode 311 connected to the first conductive post 7 and the second electrode 312 connected to the second conductive post 8. The first conductive post 7 and the second conductive post 8 are respectively connected to the circuit board 6 and both extend along a first direction. Both the diaphragm 1 and the insulating film have clearance holes through which the first conductive post 7 and the second conductive post 8 pass, facilitating assembly. At least a portion of the first electrode 311 and at least a portion of the second electrode 312 are located at the clearance holes, contacting and connecting with the first conductive post 7 and the second conductive post 8 passing through the clearance holes.

[0039] The diaphragm 1 of the loudspeaker, as the core component of electroacoustic conversion, is responsible for converting electrical signals into audible sound waves (20 Hz – 20 kHz) in audio applications. The thickness of the diaphragm 1 directly affects the resonant frequency, sensitivity, and distortion. A thinner diaphragm results in lower mass and a higher resonant frequency, which is beneficial for high-frequency response. However, excessive thinness can lead to insufficient strength, susceptibility to breakage, and decreased driving efficiency. In one embodiment, the diaphragm 1 of this application is a single-crystal silicon or silicon nitride thin film, and the thickness 'a' of the diaphragm 1 satisfies the following condition: 1.0 μm ≤ a ≤ 2.0 μm, preferably 1.5 μm. This thickness of the diaphragm enables the loudspeaker of this application to have a better high-frequency response. The high-frequency response of the loudspeaker is determined by the silicon-based diaphragm 1. By optimizing the thickness of the diaphragm 1, the loudspeaker of this application extends the operating frequency band to 60 kHz, meeting the requirements for high-fidelity audio reproduction.

[0040] In one specific embodiment, the diaphragm 1 is made of low-stress silicon-rich silicon nitride (SiNx) material with a thickness of approximately 1.5 μm. This material exhibits high mechanical stability and fatigue strength, and is well-compatible with loudspeaker manufacturing processes.

[0041] In one embodiment, the coil 31 is made of copper-nickel nanocomposite material, wherein nickel is uniformly dispersed in the form of nanoparticles in the copper matrix.

[0042] In a further embodiment, the nickel nanoparticles have a particle size of 25 nm to 50 nm.

[0043] In one embodiment, the linewidth of coil 31 is b, which satisfies: 5μm≤b≤15μm.

[0044] In one embodiment, the insulating layer 2 can be a silicon oxide or silicon nitride film, and the thickness of the insulating layer 2 is c, which satisfies: 0.5μm≤c≤1.5μm, preferably 1.0μm.

[0045] The embodiments of this application also provide a method for fabricating the electromagnetic MEMS loudspeaker described in some of the above embodiments, comprising the following steps: S1: A substrate is provided, on which a first seed layer and a first sacrificial layer are sequentially prepared, and the pattern of the coil assembly is defined on the sacrificial layer by photolithography. The substrate is a vibrating membrane.

[0046] In this step, the sacrificial layer is the first sacrificial layer, and the coil assembly is the first layer coil assembly.

[0047] In MEMS loudspeaker manufacturing, the seed layer is an extremely thin layer of conductive material, typically tens to hundreds of nanometers thick, deposited on the substrate surface. It serves as the nucleation base and conductive pathway for subsequent electroplated metal structures, such as planar voice coils. Its core function is to provide a uniform electrochemical deposition start point, allowing metals such as copper and nickel to grow "from bottom to top" along a specified pattern, ensuring the continuity, conductivity, and adhesion of the coil structure. The sacrificial layer refers to a material layer temporarily deposited during processing and ultimately selectively etched away. It is used to construct cavities or release movable structures. In later stages of the process, it can be removed using wet methods such as hydrofluoric acid etching of silicon dioxide, or dry methods such as oxygen plasma removal of polymers.

[0048] An SOI wafer is selected as the substrate. This SOI wafer comprises a bottom silicon substrate, a buried oxide layer, and a top silicon device layer. The top silicon device layer will serve as the base material for the diaphragm 1. A thin oxide layer is formed on the top silicon device layer using thermal oxidation or deposition processes, followed by sputtering of a seed layer. The seed layer can be a stack of 50 nm thick titanium (Ti) and 200 nm thick copper (Cu). Subsequently, a first sacrificial layer (photoresist) is spin-coated onto the seed layer, and the pattern openings for the first layer coil are defined on the first sacrificial layer using photolithography.

[0049] S2: An electroplating process is used to form the coil assembly within the pattern of the coil assembly. Specifically, ferromagnetic nanocomposite material is deposited within the coil pattern of the first layer, and 1J85 iron-nickel-molybdenum soft magnetic alloy is deposited within the soft magnetic core pattern of the first layer, thereby forming the first coil assembly. Specifically, using the first sacrificial layer as a mask, an electroplating process is used to deposit ferromagnetic nanocomposite material within the opening of the coil pattern to form the first coil layer, with an electroplating thickness of approximately 2 μm. 1J85 iron-nickel-molybdenum soft magnetic alloy material is deposited within the soft magnetic core pattern, with the following composition: Ni 80.2%, Mo 5.0%, Fe balance, and a thickness of 4 μm.

[0050] The electroplating process for the aforementioned coil uses a basic alkaline cyanide-free copper plating solution with added nickel nanoparticles. The average particle size of the nickel nanoparticles is 30 nm, and the concentration is 2.0 g / L. During the electroplating process, a magnetic stirrer is used to maintain uniform stirring of the plating solution, ensuring that the nickel nanoparticles are uniformly suspended and co-deposited into the seed layer. The nickel nanoparticles added to the alkaline cyanide-free copper plating solution have a particle size of 25 nm to 50 nm and a concentration of 1.5 g / L to 2.5 g / L.

[0051] Verified by SQUID (Superconducting Quantum Interferometer) magnetic measurements, the Cu-Ni nanocomposite electroplated layer prepared using this composition and process transforms from the diamagnetic properties of pure copper to significant ferromagnetism. Its saturation magnetization is sufficient to generate a millitalas (mT) magnetic field in a micrometer-scale space when a milliampere-level current is applied. This allows the magnetic fields generated when the coil is energized to superimpose or interact, forming a Lorentz force sufficient to drive the diaphragm, thus achieving complete self-driving.

[0052] S3: Remove the sacrificial layer and the uncovered first seed layer.

[0053] S4: Deposit an insulating layer on the side of the coil assembly facing away from the substrate. This insulating layer is the first insulating layer.

[0054] Specifically, the first insulating layer is deposited using the PECVD process to cover the first coil assembly.

[0055] S5: A seed layer and a sacrificial layer are sequentially fabricated on the insulating layer, and the patterns of the coil assembly and the soft magnetic core are defined using photolithography. The seed layer and the sacrificial layer are the seed layer of the second layer and the sacrificial layer of the second layer.

[0056] Specifically, a seed layer (i.e., the second seed layer) is sputtered onto the first insulating layer, followed by spin coating of the second sacrificial layer. The pattern opening of the second coil assembly is then defined on the second sacrificial layer using photolithography. This photolithography step requires the coil assembly of the first layer as an alignment marker to ensure that the coil pattern of the second layer is basically aligned with the coil assembly of the first layer, with the alignment deviation controlled within ±3μm.

[0057] S6: Repeat steps S2 to S5 according to the preset number of sub-coil layers.

[0058] Specifically, an electroplating process is used to deposit ferromagnetic nanocomposite material within the coil pattern of the second-layer coil assembly, and to deposit 1J85 iron-nickel-molybdenum soft magnetic alloy within the soft magnetic core pattern, forming the second-layer coil assembly. The second sacrificial layer and the second seed layer covered by the second sacrificial layer are then removed. Subsequent coil assembly fabrication processes are the same and will not be detailed here.

[0059] In one embodiment, the housing can be fabricated using the following steps: S1: An SOI wafer with a thickness of approximately 400 μm is provided. A back cavity is formed on its back side using a deep reactive ion etching (DRIE) process, with a back cavity depth of approximately 200-300 μm. Specifically, deep silicon etching is performed using a buried oxide layer as the etch stop layer to form the back cavity. Finally, the exposed buried oxide layer is removed.

[0060] S2: The wafer is diced into individual chips, and the electrodes of the coil assembly are connected to the packaging substrate or PCB circuit board via wire bonding or flip-chip bonding, and then connected in parallel externally. Finally, two main electrodes, A+ and A-, are brought out for connecting to the audio signal source.

[0061] Obviously, those skilled in the art can make various modifications and variations to this application without departing from the spirit and scope of this application. Therefore, if such modifications and variations fall within the scope of the claims of this application and their equivalents, this application also intends to include such modifications and variations.

Claims

1. An electromagnetic MEMS loudspeaker, characterized in that, It includes a plurality of coil assemblies and a diaphragm stacked along a first direction, wherein an insulating layer is provided between the plurality of coil assemblies. Each of the coil assemblies includes a coil and a soft magnetic core, the coil being wound around the outer periphery of the soft magnetic core; The plurality of coil assemblies are arranged in parallel, and the first direction is perpendicular to the vibrating diaphragm.

2. The electromagnetic MEMS loudspeaker according to claim 1, characterized in that, The vertical projections of the plurality of coil assemblies along the first direction completely overlap.

3. The electromagnetic MEMS loudspeaker according to claim 1, characterized in that, The coil includes a first part and a second part, both of which are bow-shaped coiled structures, and the first part and the second part are symmetrically arranged on both sides of the soft magnetic core.

4. The electromagnetic MEMS loudspeaker according to any one of claims 1 to 3, characterized in that, The number n of the coil assemblies satisfies: 2≤n≤5.

5. The electromagnetic MEMS loudspeaker according to claim 1, characterized in that, The loudspeaker also includes a housing and a mounting frame, the mounting frame being installed at an opening in the housing, and the diaphragm being installed on the mounting frame.

6. The electromagnetic MEMS loudspeaker according to claim 1, characterized in that, The loudspeaker also includes a circuit board, which is arranged along the first direction with the diaphragm and the circuit board is spaced at a predetermined distance from the diaphragm. The plurality of coil assemblies are electrically connected to the circuit board.

7. The electromagnetic MEMS loudspeaker according to claim 6, characterized in that, The coil includes a first electrode and a second electrode, and the electromagnetic MEMS loudspeaker also includes a first conductive post and a second conductive post, with the first electrode connected to the first conductive post and the second electrode connected to the second conductive post; The first conductive post and the second conductive post are respectively connected to the circuit board and both extend along the first direction. The vibrating diaphragm and the insulating diaphragm both have clearance holes through which the first conductive post and the second conductive post pass.

8. The electromagnetic MEMS loudspeaker according to claim 1, characterized in that, The vibrating membrane is a single-crystal silicon or silicon nitride thin film, and the thickness 'a' of the vibrating membrane satisfies: 1.0 μm ≤ a ≤ 2.0 μm.

9. The electromagnetic MEMS loudspeaker according to claim 1, characterized in that, The coil is made of copper-nickel nanocomposite material, wherein nickel is uniformly dispersed in the copper matrix in the form of nanoparticles.

10. The electromagnetic MEMS loudspeaker according to claim 9, characterized in that, The nickel nanoparticles have a particle size of 25 nm to 50 nm.

11. The electromagnetic MEMS loudspeaker according to claim 1, characterized in that, The linewidth of the coil is b, which satisfies the following condition: 5μm≤b≤15μm.

12. The electromagnetic MEMS loudspeaker according to claim 1, characterized in that, The insulating layer is a silicon oxide or silicon nitride thin film, and the thickness of the insulating layer is c, which satisfies: 0.5μm≤c≤1.5μm.

13. A method for fabricating an electromagnetic MEMS loudspeaker as described in any one of claims 1 to 12, characterized in that, Includes the following steps: S1: A substrate is provided, on which a seed layer and a sacrificial layer are sequentially prepared, and a pattern of a coil assembly is defined on the sacrificial layer by photolithography; the substrate is a vibrating diaphragm. S2: The coil assembly is formed within the pattern of the coil assembly using an electroplating process; S3: Remove the sacrificial layer and the uncovered seed layer; S4: Deposited insulating layer; S5: A seed layer and a sacrificial layer are sequentially prepared on the insulating layer, and the pattern of the coil assembly is defined on the sacrificial layer by photolithography. S6: Repeat steps S2 to S5 according to the preset number of sub-coil layers.

14. The method for fabricating an electromagnetic MEMS loudspeaker according to claim 13, characterized in that, Step S2: The coil assembly is formed within the pattern of the coil assembly using an electroplating process, including: depositing an alkaline cyanide-free copper plating solution within the coil pattern of the coil assembly and continuously stirring the alkaline cyanide-free copper plating solution, wherein the alkaline cyanide-free copper plating solution contains nickel nanoparticles with a particle size of 25nm to 50nm and a concentration of 1.5g / L to 2.5g / L.

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