A flat panel acoustic unit of a multi-layer hetero-composite diaphragm

Abstract

This invention discloses a planar speaker unit with a multilayer heterogeneous composite diaphragm, comprising a diaphragm, a planar voice coil, and a strip permanent magnet array. The diaphragm includes a substrate layer and a heterogeneous layer group, wherein the heterogeneous layer group comprises at least two heterogeneous sublayers with different Young's moduli disposed in different regions within the plane. The heterogeneous sublayers are disposed in the gap region of the voice coil traces and / or cover the surface of the voice coil traces. The heterogeneous sublayers include a high-mode quantum layer in the central region, a low-mode quantum layer in the edge region, a passive resonant shunt circuit composed of a piezoelectric layer and microbridge contacts, magnetorheological elastomer micro-islands, and a Ni-W alloy modulus gradient layer. Through in-plane localized mechanical control, high-frequency split vibration is effectively suppressed, the split vibration initiation frequency is delayed, the sound pressure frequency response flatness is improved, and the wear resistance and anti-electromigration performance of the voice coil traces are enhanced with minimal mass increment.

Description

Technical Field

[0001] This invention relates to the field of audio equipment technology, specifically to a flat panel speaker unit with a multilayer heterogeneous composite diaphragm. Background Technology

[0002] Planar magnetic speakers rely on the electromagnetic coupling between a planar voice coil and a permanent magnet array to achieve electroacoustic conversion, offering theoretical advantages such as lightweight diaphragm and low split vibration. However, as diaphragm size increases and the operating frequency band expands to higher frequencies, the isotropic in-plane mechanical distribution of traditional uniform material diaphragms struggles to simultaneously meet the requirements of high compliance at low frequencies and high rigidity at high frequencies.

[0003] Existing technologies often improve high-frequency response by increasing the overall diaphragm thickness or adding a global damping layer. While these methods increase stiffness, they also significantly increase diaphragm mass, leading to decreased sensitivity and deteriorated transient response. Other technologies employ localized reinforcing rings or overall coatings, but their in-plane mechanical modulation precision is insufficient, failing to effectively suppress the various vibration modes of the diaphragm. Therefore, achieving localized, non-uniform mechanical property control within the diaphragm surface while maintaining a low overall diaphragm mass has become a key technological bottleneck for further improving the acoustic performance of planar magnetic speakers. Summary of the Invention

[0004] This invention provides a planar speaker unit with a multilayer heterogeneous composite diaphragm. The planar speaker unit includes a diaphragm, a planar voice coil disposed on at least one side of the diaphragm, and a strip permanent magnet array located on both sides of the diaphragm and cooperating with the planar voice coil. The strip permanent magnet array generates a horizontal static magnetic field parallel to the surface of the diaphragm. The straight segments of the serpentine routing of the planar voice coil are perpendicular to the long axis of the strip permanent magnets, so that when the audio current passes through the serpentine routing, a Lorentz driving force perpendicular to the surface of the diaphragm is generated.

[0005] The diaphragm includes a substrate layer and a heterogeneous layer group. The heterogeneous layer group includes at least two types of heterogeneous sublayers respectively disposed in different regions within the plane of the diaphragm. The at least two types of heterogeneous sublayers have different Young's moduli, and at least a portion of the heterogeneous sublayers are disposed in the trace gap region of the planar voice coil or cover at least a portion of the trace segment surface of the planar voice coil.

[0006] The heterolayer group includes a high-mode quantum layer located in the central region of the diaphragm and a low-mode quantum layer located in the edge region of the diaphragm. The Young's modulus of the high-mode quantum layer is greater than 10 GPa, the Young's modulus of the low-mode quantum layer is less than 1 GPa, and an intermediate transition region without heterolayers is formed between the high-mode quantum layer and the low-mode quantum layer.

[0007] In one specific implementation, the high-mode quantum layer is an inorganic oxide nanolayer formed in the wiring gap region by sputtering or atomic layer deposition, and the low-mode quantum layer is a viscoelastic polymer nanolayer formed in the wiring gap region by spin coating or inkjet printing. The inorganic oxide nanolayer is SiO2 or Al2O3, with a thickness of 30 nm to 100 nm; the viscoelastic polymer nanolayer is fluorosilicone rubber, polyurethane acrylate, or a polydimethylsiloxane derivative, with a thickness of 30 nm to 100 nm. The preparation method is as follows:

[0008] Step 1, Substrate preparation: A 2.0 μm thick biaxially oriented polyimide film is selected as the substrate layer. The two sides of the substrate layer are treated with oxygen plasma. The treatment parameters are: Ar / O2 volume flow ratio 9:1, radio frequency power 80W, and treatment time 120 s, so that the surface energy is increased from about 40 mN / m to more than 50 mN / m.

[0009] Step 2, Voice Coil Fabrication: On the magnet side surface of the substrate layer, a 20 nm Cr adhesion layer and a 100 nm Cu seed layer are sequentially deposited by electron beam evaporation; positive photoresist AZ is then spin-coated. (R) From 1512 to a thickness of 1.2 μm, by contact exposure (wavelength 365 nm, dose 120 mJ / cm²). 2 ) and development (AZ) (R) A serpentine trace pattern is defined using 300 MIF developer (60 s), with a line width of 30 μm and a line spacing of 90 μm. The straight segments of the traces are perpendicular to the long axis of the strip permanent magnet. Electroplating is performed using copper sulfate electrolyte at a current density of 2 A / dm³. 2 The temperature was 25°C, and the electroplating time was 8 minutes to achieve a total Cu layer thickness of 100 nm; the adhesive was removed by ultrasonic removal with acetone for 3 minutes, followed by Ar... + Ion beam etching removes the Cu seed layer from the exposed area, forming an independent serpentine voice coil trace. The DC resistance of the voice coil is 30 Ω to 60 Ω.

[0010] Step 3, High Modulus Filling in the Central Region: Spin-coat a negative photoresist, ma-N 2400, to a thickness of 1.5 μm in the trace gap region on the air-side or magnet-side surface of the substrate layer; expose only the central region trace gap with a radius r < 12 mm through overlay exposure, with an exposure alignment accuracy better than 2 μm; develop with developer ma-D 525 for 90 s; deposit SiO2 using RF magnetron sputtering with a target purity of 99.99%, Ar atmosphere, sputtering power of 150 W, deposition rate of 5 nm / min, and deposition time of 10 min to form a 50 nm thick SiO2 nanolayer; perform a lift-off by immersing in N-methylpyrrolidone at 60°C for 20 min, retaining only the SiO2 nanoislands within the trace gaps as the high-modulus quantum layer.

[0011] Step 4, Low-modulus filling of edge areas: Positive photoresist is spin-coated onto the corresponding surface of the substrate layer, and the edge area trace gaps with an exposure radius r > 40 mm are exposed by overlay etching; after development, a micro piezoelectric inkjet printhead is used to print a fluorosilicone rubber prepolymer onto the exposed area, wherein the prepolymer is Dow Corning (R) After dilution, the viscosity of LS~2840 was adjusted to 800 cP, the droplet volume was 10 pL, and the nozzle drive frequency was 20 kHz. It was then heat-cured at 80°C for 40 min to crosslink but not completely vulcanize the fluorosilicone rubber, retaining a loss factor of tanδ≈0.5@1 kHz. The fluorosilicone rubber was then lifted off using acetone ultrasound, retaining only the fluorosilicone rubber nanolayer in the wiring gap as the low-mode quantum layer.

[0012] Step 5, post-processing: The entire diaphragm surface is cleaned with oxygen plasma to remove residual adhesive, and then a 5 nm thick parylene C protective layer is sprayed using chemical vapor deposition at room temperature.

[0013] Piezoelectric shunt damping integrated diaphragm

[0014] The diaphragm further includes a piezoelectric layer and piezoelectric electrodes. The piezoelectric layer is located between the substrate layer and the planar voice coil. The piezoelectric electrodes include a first electrode and a second electrode. The first electrode is disposed on the side of the piezoelectric layer closer to the substrate layer. The second electrode is electrically connected to at least a portion of the planar voice coil's traces via microbridge contacts distributed in the trace gap region, such that the inherent inductance of the piezoelectric layer and at least a portion of the planar voice coil's traces forms a passive parallel resonant shunt circuit. The first electrode is connected to the other end of the voice coil trace via a lead-out electrode in the trace gap, or the first electrode is connected to ground at the common terminal of the voice coil.

[0015] In one specific implementation, the piezoelectric layer is a c-axis preferred-oriented ZnO thin film deposited by sputtering, with a thickness of 50 nm to 150 nm; the diameter of the microbridge contacts is 3 μm to 10 μm, and the in-plane spacing is 1 mm to 5 mm; the resonant frequency of the passive parallel resonant shunt circuit corresponds to the target segmented vibration frequency of the diaphragm.

[0016] Preparation method:

[0017] Step 1, substrate and bottom electrode fabrication: A 2.0 μm thick polyimide film is selected as the substrate layer; on the magnet side surface of the substrate layer, a 10 nm Cr adhesion layer and a 10 nm Au conductive layer are sequentially deposited by electron beam evaporation as the first electrode; the first electrode is patterned into a ring pattern by photolithography and ion beam etching, the width of the ring pattern being 80 μm, covering the trace gap area of ​​the planar voice coil.

[0018] Step 2, piezoelectric layer preparation: On the surface of the first electrode, a c-axis preferred oriented ZnO thin film is deposited as the piezoelectric layer using RF magnetron sputtering. The sputtering target is a ZnO ceramic target with a purity of 99.99% and doped with 1 wt% Al2O3 to improve conductivity. The sputtering atmosphere is a mixture of Ar and O2 gas with a volume flow rate ratio of Ar:O2=80:20, a total gas pressure of 0.5 Pa, an RF sputtering power of 100 W, a substrate temperature of 150°C, a deposition time of 25 min, and a deposition thickness of 100 nm. X-ray diffraction confirms that the intensity ratio of the (002) crystal plane diffraction peak of the ZnO thin film is greater than 90%, ensuring piezoelectric activity.

[0019] Step 3, Piezoelectric layer patterning: Positive photoresist is spin-coated onto the ZnO thin film surface. The ZnO thin film is patterned into a ring-shaped island array that coincides with the first electrode by photolithography and wet etching (dilute HCl solution, concentration 0.5 mol / L, etching time 15 s). The width of the ring island is 60 μm and the spacing between adjacent ring islands is 2 mm to expose the area for subsequent formation of microbridge contacts.

[0020] Step 4, simultaneous fabrication of the voice coil and microbridge contacts: On the patterned ZnO film and the exposed first electrode surface, a 20 nm Cr adhesion layer and a 100 nm Cu seed layer are sequentially sputtered and deposited; positive photoresist is spin-coated to a thickness of 1.2 μm, and a serpentine trace pattern and a microbridge contact pattern are defined by overlay exposure. The serpentine trace has a linewidth of 30 μm and a line spacing of 90 μm. The microbridge contacts have a diameter of 5 μm, are distributed in the trace gap region, and have an in-plane spacing of 2 mm; Cu is electroplated to thicken the total thickness to 100 nm; the Cu layer at the microbridge contacts directly covers the first electrode exposed area on the ZnO film surface, forming an ohmic contact between the second electrode and the voice coil trace; after photoresist removal, Ar is used... + Ion beam etching removes excess Cu seed layer, forming independent serpentine voice coil traces and microbridge contact arrays. The first electrode is connected to the other end of the voice coil trace via a lead-out electrode through the trace gap, or the first electrode is connected to ground with the common terminal of the voice coil.

[0021] Step 5, post-processing: The entire diaphragm surface is cleaned with oxygen plasma to remove residual adhesive and organic contaminants; a 5 nm thick parylene C protective layer is sprayed using chemical vapor deposition.

[0022] A continuous transparent conductive layer (such as ITO 5 nm~20 nm or an ultrathin Au layer 3 nm~10 nm) is sputtered and deposited on the entire surface of the ZnO piezoelectric layer as a second electrode. This continuous second electrode forms an ohmic contact with microbridge contacts distributed in the trace gaps, and is then electrically connected to the voice coil trace through the microbridge contacts to form a passive parallel resonant shunt circuit.

[0023] The resonant frequency of the passive parallel resonant shunt circuit is determined by the inherent inductance L of the voice coil trace and the equivalent capacitance C of the piezoelectric layer. p Jointly decided, satisfying the relational expression By adjusting the in-plane spacing of the microbridge contacts and the deposition thickness of the ZnO film, f0 is aligned with the target segmented vibration frequency of the diaphragm.

[0024] Local reinforcement of magnetorheological elastomer micro-islands

[0025] The heterostructure also includes magnetorheological elastomer micro-islands, which are discretely distributed in the trace gap region of the planar voice coil. The thickness of the magnetorheological elastomer micro-islands is 50 nm to 100 nm, and the in-plane equivalent diameter is 30 μm to 60 μm.

[0026] In one specific implementation, the magnetorheological elastomer micro-island, under the action of the horizontal static magnetic field generated by the strip permanent magnet array, has an in-plane shear modulus that is more than 10 times higher than that in the zero magnetic field state, and the distribution area of ​​the magnetorheological elastomer micro-island coincides with the magnet gap area of ​​the strip permanent magnet array on the in-plane projection.

[0027] Preparation method:

[0028] Step 1, Substrate and Voice Coil Preparation: Prepare a polyimide diaphragm substrate with serpentine Cu voice coil traces.

[0029] Step 2, Surface Modification: The magnet side surface of the diaphragm is treated with oxygen plasma with the following parameters: power 100 W, O2 flow rate 50 sccm, time 180 s; then immediately immersed in a 1 wt% 3-aminopropyltriethoxysilane anhydrous ethanol solution, reacted at room temperature for 30 min; rinsed with deionized water and then... N2 The surface of the polyimide is dried to form a silanized monolayer, which improves the adhesion of subsequent silicone polymers.

[0030] Step 3, Magnetorheological elastomer ink formulation: using polydimethylsiloxane prepolymer Sylgard (R) The matrix is ​​composed of 184 (component A to component B in a mass ratio of 10:1), incorporating 28% carbonyl iron powder (BASF Carbonyl Iron PowderOM, particle size 3 μm~5 μm, surface passivated with phosphoric acid); and 2 wt% fumed silica (Aerosil) is added. (R) 200 is used as a thixotropic agent; the carbonyl iron powder is uniformly dispersed in the polydimethylsiloxane matrix by grinding three times with a roller gap of 25 μm using a three-roll mill; the viscosity is adjusted to 800 cP~1200 cP (25°C) by dilution with xylene.

[0031] Step 4, Micro-inkjet printing: Using a piezoelectric inkjet printhead (nozzle diameter 50 μm, driving voltage 30 V, pulse width 8 μs), the magnetorheological elastomer ink is printed onto the gap area of ​​the planar voice coil. The printing path is aligned using a visual alignment system with the Cu serpentine traces as a reference, covering only the in-plane projection area of ​​the magnet gap area of ​​the strip permanent magnet array on the diaphragm surface. The volume of a single droplet is approximately 25 pL, with a landing accuracy of ±5 μm. After printing, the droplets spread under surface tension to form flat micro-islands with an in-plane equivalent diameter of approximately 40 μm and a thickness of approximately 80 nm. The center-to-center distance between adjacent micro-islands is 150 μm, arranged in a hexagonal close-packed distribution.

[0032] Step 5, Curing: Place the printed diaphragm on an 80°C hot plate for 45 min to cure, allowing the polydimethylsiloxane to complete the crosslinking reaction; no external magnetic field is applied during the curing process to maintain the isotropic distribution of the carbonyl iron powder in the micro-islands.

[0033] Step 6, Magnetic field activation: The cured diaphragm is installed into the magnetic circuit of the strip permanent magnet array. The strip permanent magnet is an NdFeB permanent magnet with a surface magnetic field strength of 0.8 T to 1.2 T. Under the action of the horizontal static magnetic field, the carbonyl iron powder forms a chain-like aggregate structure along the magnetic field direction, thereby increasing the in-plane shear modulus of the micro-island from about 1.5 MPa to about 25 MPa to 30 MPa.

[0034] Radial modulus gradient of ion implantation modified substrate

[0035] The substrate layer is a polymer film modified by ion implantation. The substrate layer has different ion implantation doses in different regions of the plane, so that the Young's modulus of the substrate layer is non-uniformly distributed in the plane.

[0036] In one specific implementation, the ion implantation dose in the central region (radius r < 15 mm) of the substrate layer is higher than the ion implantation dose in the edge region (radius r > 40 mm) of the substrate layer, such that the Young's modulus of the central region is 20% to 50% higher than that of the edge region, and the total thickness of the substrate layer remains unchanged before and after ion implantation.

[0037] Preparation method:

[0038] Step 1, Substrate preparation: Select a 2.0 μm thick polyimide film as the original substrate.

[0039] Step 2, Ion implantation dose gradient formation: using Si + The original substrate was irradiated with an ion beam at an ion energy of 100 keV and a beam current density of 5 μA / cm. 2 The injection area is controlled by a movable mask with radially tapered openings, such that the cumulative injection dose in the central region is 1×10⁻⁶. 15 ions / cm 2 The cumulative injection dose in the edge region is 3 × 10⁻⁶. 14 ions / cm 2 The middle region has a continuous gradient transition; during the injection process, the temperature of the original substrate is controlled below 80°C by back-side helium cooling to prevent thermal degradation.

[0040] Step 3, post-processing: After ion implantation, the substrate surface is cleaned with deionized water to remove any possible sputtering deposits; annealing is performed at 150°C for 30 min to allow the free radicals generated by irradiation to fully react and stabilize.

[0041] Step 4, voice coil fabrication: serpentine Cu voice coil traces are fabricated on the surface of the ion-implanted modified substrate layer.

[0042] The ion implantation modification breaks some CN and CC bonds in the polyimide molecular chain and induces a cross-linking reaction, forming a higher density three-dimensional cross-linked network in the central region, thereby increasing the local Young's modulus; simultaneously, because the implantation dose is controlled in the low-dose region (<2×10⁻⁶), the local Young's modulus is improved. 15 ions / cm 2 The substrate layer did not undergo significant carbonization and embrittlement, and the elongation at break remained above 30%.

[0043] Modal splitting of asymmetric biaxially oriented substrates

[0044] The substrate layer is a biaxially stretched polymer film with in-plane anisotropy. The Young's modulus E1 of the substrate layer in the first direction and the Young's modulus in the second direction perpendicular to the first direction are... E2 The ratio is 1.1 to 1.4, and the first direction forms a 45° angle with the extension direction of the straight line segment of the serpentine routing of the planar voice coil.

[0045] In one specific implementation, the substrate layer is a polyimide film or a polyethylene terephthalate film, and the in-plane anisotropy is obtained by controlling the difference between the longitudinal stretch ratio and the transverse stretch ratio; the longitudinal stretch ratio is 3.2~3.8, and the transverse stretch ratio is 2.5~3.0.

[0046] Preparation method:

[0047] Step 1, casting: The polyamic acid precursor solution (solid content 15 wt%, solvent is N,N-dimethylacetamide) is extruded through a slit die onto a stainless steel strip to form a wet film with a thickness of 200 μm; it is then dried at 80°C for 10 min to remove some of the solvent.

[0048] Step 2, Asymmetric Biaxial Stretching: The wet film is peeled from the stainless steel strip and fed into a biaxial stretching machine; first, longitudinal stretching is performed at a stretching temperature of 120°C and a stretch ratio of 3.5; then, transverse stretching is performed at a stretching temperature of 130°C and a stretch ratio of 2.7; the ratio of longitudinal to transverse stretching speeds is 1.2:1; immediately after stretching, it is heat-set at 280°C for 60 seconds to imidize the polyamic acid and form polyimide; the longitudinal Young's modulus E of the resulting film is... MD ≈3.8 GPa, transverse Young's modulus ETD ≈2.9 GPa, ratio E MD / E TD ≈1.31.

[0049] Step 3, Orientation Alignment: Cut the asymmetric biaxially oriented film into a circular diaphragm, ensuring that the longitudinal direction (high modulus direction) forms a 45° angle with the extension direction of the straight line segment of the serpentine routing of the planar voice coil during cutting.

[0050] Step 4, voice coil fabrication: a serpentine Cu voice coil trace is fabricated on the surface of the substrate layer.

[0051] The in-plane anisotropy causes the axisymmetric bending modes of the diaphragm to split, and the originally degenerate (m,n) mode pair splits into two sub-modes with different frequencies, and the frequency difference Δf between the sub-modes is proportional to the Young's modulus ( ). E1 / E2 The high modulus direction is proportional to the square root of the π / 4; by aligning the high modulus direction with the 45° direction, the split sub-mode vibration modes are spatially staggered, so that the sound pressure radiation of the diaphragm in the axial direction exhibits a diffusion effect.

[0052] Voice coil trace surface modulus gradient layer

[0053] The heterogeneous layer group further includes a modulus gradient sublayer covering at least a portion of the trace surface of the planar voice coil. The Young's modulus of the modulus gradient sublayer is different from the Young's modulus of the main material of the planar voice coil, and the modulus gradient sublayer is non-uniformly distributed in the plane of the diaphragm.

[0054] In one specific implementation, the main material of the planar voice coil is Cu, and the modulus gradient sublayer is a Ni-W alloy nanolayer formed by selective electroplating with a thickness of 20 nm to 50 nm. The modulus gradient sublayer only covers the surface of the trace segment in the central region of the diaphragm.

[0055] Preparation method:

[0056] Step 1, Substrate and Voice Coil Fabrication: A polyimide substrate with a thickness of 2.0 μm and a serpentine Cu voice coil trace with a thickness of 100 nm are prepared. The linewidth of the voice coil trace is 30 μm and the line spacing is 90 μm.

[0057] Step 2, Selective Masking: Spin-coating positive photoresist AZ onto the surface of the voice coil traces. (R) The thickness ranges from 1512 to 1.5 μm; through overlay exposure, only the surface of the trace segments in the central region with a radius r < 15 mm is exposed, while the surface of the trace segments in the edge region with a radius r > 40 mm is covered and protected by the photoresist; the exposure alignment accuracy is better than 2 μm.

[0058] Step 3, selective electroplating of Ni-W alloy: The exposed diaphragm is immersed in a nickel sulfamate-tungstate electroplating solution, the composition of which is: 200 g / L nickel sulfamate, 30 g / L sodium tungstate, 40 g / L citric acid, 10 g / L nickel chloride, pH 3.5, temperature 45°C; the Cu voice coil trace is used as the cathode, the insoluble anode, and the current density is 1 A / dm³. 2 Electroplating time is 5 min to deposit a 30 nm Ni-W amorphous alloy nanolayer on the exposed central region trace surface; the atomic fraction of W in the Ni-W alloy is 25%~35%, and the Young's modulus is about 350 GPa.

[0059] Step 4, Resin Removal and Cleaning: Use acetone for ultrasonic removal for 3 minutes to remove the photoresist covering the trace surface of the edge area, exposing the original Cu trace surface; rinse with deionized water and dry with N2.

[0060] Step 5, post-processing: The entire diaphragm surface is cleaned with oxygen plasma to remove residual adhesive; a 5 nm thick parylene C protective layer is sprayed using chemical vapor deposition.

[0061] Mechanism of action and unexpected technical effects: The Ni-W alloy nanolayer on the surface of the central region trace increases the local equivalent bending stiffness of the voice coil-substrate composite structure by approximately 2.5 times, while the edge region maintains the lower modulus of Cu, forming a radial modulus gradient. Simultaneously, due to the Vickers hardness of Ni-W alloy exceeding 600 HV, far higher than Cu's 120 HV, the wear resistance and anti-electromigration properties of the central region trace are significantly improved. The areal density increment of the Ni-W alloy layer is only 0.0004 g / cm³. 2 The impact on the total mass of the diaphragm is less than 2%, but the starting frequency of the high-frequency split vibration is pushed back by about 2 kHz.

[0062] The beneficial effects of this invention are as follows:

[0063] This invention employs at least two heteroproton layers with different Young's moduli in different regions within the diaphragm surface, and positions these heteroproton layers in the voice coil trace gap region or covering the voice coil trace surface, achieving localized and precise control of the diaphragm's mechanical properties. The high-mode quantum layer in the central region significantly enhances the equivalent bending stiffness of the diaphragm's central area, effectively delaying the high-frequency split vibration initiation frequency and suppressing the split vibration amplitude; the low-mode quantum layer in the edge region maintains the diaphragm's edge compliance, ensuring the linearity of low-frequency sound pressure output and diaphragm displacement.

[0064] The integrated piezoelectric shunt damping scheme utilizes the inherent inductance of the voice coil traces and the equivalent capacitance of the piezoelectric layer to form a passive parallel resonant circuit. This creates impedance matching at the target segmented vibration frequency, converting mechanical vibration energy into electrical energy and dissipating it as Joule heat. Narrow-band vibration suppression can be achieved without external circuitry. Magnetorheological elastomer micro-islands undergo magnetohardening under the influence of a horizontal static magnetic field provided by the speaker permanent magnet. Their in-plane shear modulus increases by more than tenfold, and the hardened region coincides with the projection of the magnet gap, achieving adaptive local stiffness enhancement.

[0065] The selectively electroplated Ni-W alloy nanolayer on the voice coil traces creates a modulus gradient in the central region, increasing the local equivalent bending stiffness by approximately 2.5 times. Simultaneously, it delays the high-frequency split vibration onset frequency by approximately 2 kHz, with an areal density increment of less than 0.0004 g / cm³. 2 The impact on the total mass of the diaphragm is less than 2%. Furthermore, the high hardness of the Ni-W alloy significantly improves the wear resistance and anti-electromigration properties of the voice coil wiring, enhancing the long-term operational reliability of the speaker unit. These various heterolayers can be implemented independently or in combination, enabling the planar magnetic sound unit to achieve a flatter sound pressure level frequency response, lower harmonic distortion, and superior durability across a wide frequency range. Attached Figure Description

[0066] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0067] Figure 1 Schematic diagram of the overall structure of a flat panel speaker unit;

[0068] Figure 2 Schematic diagram of a partial structure of a multilayer heterogeneous composite diaphragm;

[0069] Figure 3 Schematic diagram of a partial cross-section of a multilayer heterogeneous composite diaphragm;

[0070] Figure 4 Schematic diagram of a partial structure of a piezoelectric shunt damping integrated diaphragm;

[0071] Figure 5 Schematic diagram of the micro-island distribution in a magnetorheological elastomer;

[0072] Figure 6 A schematic diagram of the local structure of the modulus gradient layer on the surface of the voice coil trace.

[0073] Figure label:

[0074] 1 External magnetic circuit, 2 Diaphragm, 3 Circuit, 4 Internal magnetic circuit, 20 Substrate layer, 21 High-mode quantum layer, 22 Intermediate transition region, 23 Low-mode quantum layer, 24 Parylene C protective layer, 25 First electrode, 26 ZnO piezoelectric layer, 27 Microbridge contact, 28 Pathway, 29 Ni-W alloy nanolayer, 31 Voice coil trace, 32 Magnetorheological elastomer micro-island. Detailed Implementation

[0075] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings.

[0076] Example 1: Multilayer heterogeneous composite diaphragm

[0077] See Figure 1 and Figure 2 , Figure 3 This embodiment provides a planar speaker unit with a multilayer heterogeneous composite diaphragm. The planar speaker unit includes a diaphragm 2, a circuit 3 (i.e., voice coil trace 31) disposed on at least one side surface of the diaphragm 2, and an outer magnetic circuit 1 and an inner magnetic circuit 4 located on both sides of the diaphragm 2 and cooperating with the circuit 3. The array of bar permanent magnets in the outer magnetic circuit 1 and the inner magnetic circuit 4 generates a horizontal static magnetic field parallel to the surface of the diaphragm 2. The straight segments of the serpentine traces of the circuit 3 are perpendicular to the long axis of the bar permanent magnets, so that when audio current passes through, a Lorentz driving force perpendicular to the surface of the diaphragm 2 is generated.

[0078] The diaphragm 2 includes a substrate layer 20 and a heterogeneous layer group. The heterogeneous layer group includes at least two types of heterogeneous sublayers respectively disposed in different regions within the surface of the diaphragm 2, and at least a portion of the heterogeneous sublayers are disposed in the wiring gap region of the line 3.

[0079] The preparation method is as follows:

[0080] Step 1, Substrate preparation: A 2.0 μm thick biaxially oriented polyimide film was selected as the substrate layer 20. The two sides of the film were treated with oxygen plasma with an Ar / O2 volume flow rate ratio of 9:1, an RF power of 80 W, and a treatment time of 120 s. The surface energy was increased from about 40 mN / m to 55 mN / m.

[0081] Step 2, voice coil fabrication: On the magnet side surface of the substrate layer 20, a 20 nm Cr adhesion layer and a 100 nm Cu seed layer are sequentially deposited by electron beam evaporation; positive photoresist AZ 1512 is spin-coated to a thickness of 1.2 μm, and then exposed by contact exposure (wavelength 365 nm, dose 120 mJ / cm²). 2The serpentine pattern is defined by developing (AZ 300 MIF developer, 60 s), with a line width of 30 μm and a line spacing of 90 μm. The straight segments of the serpentine lines are perpendicular to the long axis of the strip permanent magnet. Electroplating is performed using copper sulfate electrolyte at a current density of 2 A / dm³. 2 The temperature was 25°C, and the electroplating time was 8 min, resulting in a total Cu layer thickness of 100 nm. The adhesive was removed by ultrasonic removal with acetone for 3 min, followed by Ar plating. + Ion beam etching removes the Cu seed layer in the exposed area, forming an independent serpentine voice coil trace 31 with a DC resistance of 45 Ω.

[0082] Step 3, High Modulus Filling in the Central Region: In the trace gap region on the air-side surface of the substrate layer 20, spin-coat a negative photoresist ma-N 2400 to a thickness of 1.5 μm; through overlay exposure, only expose the trace gap in the central region with a radius r < 12 mm, with an exposure alignment accuracy better than 2 μm; develop with developer ma-D 525 for 90 s; deposit SiO2 using RF magnetron sputtering with a target purity of 99.99%, Ar atmosphere, sputtering power of 150 W, deposition rate of 5 nm / min, and deposition time of 10 min to form a 50 nm thick SiO2 nanolayer; perform lift-off by immersing in N-methylpyrrolidone at 60°C for 20 min, retaining only the SiO2 nanoislands in the trace gap as the high-modulus quantum layer 21.

[0083] Step 4, Low-modulus filling of the edge region: Positive photoresist is spin-coated onto the corresponding surface of the substrate layer 20, and the edge region trace gaps with an exposure radius r>40 mm are exposed by overlay. After development, a micro piezoelectric inkjet printhead is used to print a fluorosilicone rubber prepolymer onto the exposed area. The prepolymer is Dow Corning LS-2840 diluted to a viscosity of 800 cP, with a droplet volume of 10 pL and a printhead drive frequency of 20 kHz. It is then heat-cured at 80°C for 40 min to crosslink but not completely vulcanize the fluorosilicone rubber, retaining a loss factor tanδ≈0.5@1 kHz. Acetone is used for ultrasonic lift-off, retaining only the fluorosilicone rubber nanolayer within the trace gap as the low-modulus quantum layer 23.

[0084] Step 5, post-processing: The entire surface of the diaphragm 2 is cleaned with oxygen plasma to remove residual adhesive, and then a 5 nm thick parylene C protective layer 24 is sprayed by chemical vapor deposition at room temperature.

[0085] Regarding the width design of the intermediate transition region 22, in this embodiment, the high-mode quantum layer 21 is distributed in the central region with a radius r < 12 mm, and the low-mode quantum layer 23 is distributed in the edge region with a radius r > 40 mm. The intermediate transition region 22 has a width of 12 mm ≤ r ≤ 40 mm and a radial width of 28 mm. This width allows for a continuous transition between the high modulus (12.5 GPa) in the central region and the low modulus (0.6 GPa) in the edge region through the mechanical properties (3.2 GPa) of the substrate layer 20 itself. If the radial width of the intermediate transition region 22 is less than 5 mm, a significant modulus jump will occur at the interface between the high-mode quantum layer 21 and the low-mode quantum layer 23, inducing additional local bending modes. If the radial width is greater than 35 mm, the mechanical control effect between the central region and the edge region will be weakened, and the delay of the high-frequency split vibration initiation frequency will decrease by approximately 30%.

[0086] Scanning electron microscopy (SEM) revealed that the high-mode quantum layer 21 and the low-mode quantum layer 23 are discretely filled within the trace gaps of the voice coil trace 31, forming an unfilled intermediate transition region 22 with a radius between 12 mm and 40 mm. Atomic force microscopy (AFM) nanoindentation testing showed that the equivalent Young's modulus of the high-mode quantum layer 21 region was 12.5 GPa, the equivalent Young's modulus of the low-mode quantum layer 23 region was 0.6 GPa, and the equivalent Young's modulus of the intermediate transition region 22 was approximately 3.2 GPa, which is essentially the same as that of the substrate layer 20.

[0087] The planar speaker unit described in this embodiment was assembled in a standard IEC 60318-4 coupling cavity for sound pressure frequency response testing (excitation voltage 1 Vrms, sweep range 20 Hz–50 kHz). The results show that, compared to the uniform diaphragm of Comparative Example 1 described later, the sound pressure fluctuation in the 8 kHz–15 kHz frequency band of this embodiment was reduced from ±4.2 dB to ±1.1 dB, and the high-frequency split vibration onset frequency was delayed from 8.0 kHz to 10.6 kHz, proving that the multilayer heterogeneous composite diaphragm effectively suppressed split vibration.

[0088] Example 2: Piezoelectric shunt damping integrated diaphragm

[0089] See Figure 4This embodiment provides a piezoelectric shunt damping integrated diaphragm. The diaphragm 2 further includes a piezoelectric layer and piezoelectric electrodes. The piezoelectric layer is located between the substrate layer 20 and the voice coil trace 31. The piezoelectric electrodes include a first electrode 25 and a second electrode. The first electrode 25 is disposed on the side of the piezoelectric layer closer to the substrate layer 20. The second electrode is electrically connected to at least a portion of the voice coil trace 31 through microbridge contacts 27 distributed in the trace gap region of the voice coil trace 31, such that the inherent inductance of the piezoelectric layer and at least a portion of the voice coil trace 31 forms a passive parallel resonant shunt circuit. A path 28 is formed between the microbridge contacts 27 and the voice coil trace 31. The first electrode is connected to the other end of the voice coil trace through a lead-out electrode in the trace gap, or the first electrode is connected to the common terminal of the voice coil and grounded.

[0090] The preparation method is as follows:

[0091] Step 1, substrate and bottom electrode fabrication: A 2.0 μm thick polyimide film is selected as the substrate layer 20; on the magnet side surface of the substrate layer 20, a 10 nm Cr adhesion layer and a 10 nm Au conductive layer are sequentially deposited by electron beam evaporation as the first electrode 25; the first electrode 25 is patterned into a ring pattern by photolithography and ion beam etching, the width of the ring pattern being 80 μm, covering the trace gap area of ​​the voice coil trace 31.

[0092] Step 2, piezoelectric layer preparation: On the surface of the first electrode 25, a c-axis preferred oriented ZnO thin film is deposited as the piezoelectric layer 26 by RF magnetron sputtering. The sputtering target is a ZnO ceramic target with a purity of 99.99% and doped with 1 wt% Al2O3. The sputtering atmosphere is a mixture of Ar and O2 gas with a volume flow rate ratio of Ar:O2=80:20, a total gas pressure of 0.5 Pa, an RF sputtering power of 100 W, a substrate temperature of 150°C, a deposition time of 25 min, and a deposition thickness of 100 nm. X-ray diffraction detection shows that the intensity ratio of the (002) crystal plane diffraction peak of the ZnO thin film is 92%.

[0093] Step 3, Piezoelectric layer patterning: Positive photoresist is spin-coated onto the ZnO thin film surface. The ZnO thin film is then patterned into a ring-shaped island array overlapping the first electrode 25 using photolithography and wet etching (dilute HCl solution, concentration 0.5 mol / L, etching time 15 s). The width of each ring island is 60 μm, and the spacing between adjacent ring islands is 2 mm. The first electrode is connected to the other end of the voice coil trace via a lead-out electrode through the trace gap, or the first electrode is connected to ground via the common terminal of the voice coil.

[0094] Step 4, simultaneous fabrication of the voice coil and microbridge contacts: A 20 nm Cr adhesion layer and a 100 nm Cu seed layer are sequentially sputtered and deposited on the patterned ZnO thin film and the exposed first electrode 25 surface; positive photoresist is spin-coated to a thickness of 1.2 μm; a serpentine trace pattern and a microbridge contact pattern are defined by overlay exposure. The serpentine trace has a linewidth of 30 μm and a line spacing of 90 μm. The microbridge contacts 27 have a diameter of 5 μm, are distributed in the trace gap region, and have an in-plane spacing of 2 mm; Cu is electroplated to thicken the total thickness to 100 nm; the Cu layer at the microbridge contacts 27 directly covers the exposed area of ​​the first electrode 25 on the ZnO thin film surface, forming an ohmic contact between the second electrode and the voice coil trace 31; after photoresist removal, Ar is used... + Ion beam etching removes excess Cu seed layer, forming an independent array of serpentine voice coil traces 31 and microbridge contacts 27.

[0095] Step 5, post-processing: The entire surface of the diaphragm 2 is cleaned with oxygen plasma to remove residual adhesive and organic contaminants; a 5 nm thick parylene C protective layer 24 is sprayed using chemical vapor deposition.

[0096] In the serpentine routing of the voice coil trace 31, the trace segment between two adjacent microbridge contacts 27 is defined as a resonant unit. The in-plane spacing of the microbridge contacts 27 is 2 mm. After deducting the diameter of the microbridge contacts themselves (5 μm), the effective trace length of a single resonant unit is approximately 1.995 mm. The inherent inductance L of this trace segment is determined by the trace geometry and the permeability of Cu, and is measured to be 2.05 μH.

[0097] The equivalent capacitance Cp of the piezoelectric layer 26 is determined by both the dielectric properties of the ZnO thin film and the effective electrode area. The relative permittivity ε of ZnO... r Using a value of 8.5~10.2 (calculated as 9.0 in this embodiment), the width of a single annular island is 60 μm. With an average radius of 20 mm, its effective electrode area A≈7.54 mm². 2 According to the parallel plate capacitance formula Cp'=ε0ε r A / d, where ε0 = 8.854 × 10 -12 With F / m and d=100 nm, the capacitance of a single ring island is calculated to be approximately 6.0 nF. Since each ring island is connected in parallel with the voice coil trace 31 through the microbridge contact 27, and the total equivalent capacitance of the ring island array effectively participating in resonance is approximately 156 pF after series-parallel conversion, it is consistent with the measured value.

[0098] Although the microbridge contacts 27 are discretely distributed, their in-plane spacing of 2 mm is much smaller than the diaphragm bending wavelength (approximately 18 mm) corresponding to the target frequency of 8.91 kHz, and the thickness of the ZnO piezoelectric layer 26 (100 nm) is much smaller than the spacing of the microbridge contacts 27. Under these conditions, adjacent microbridge contacts 27 form a quasi-continuous equipotential surface on the upper surface of the ZnO thin film through the edge coupling effect of the electric field in the piezoelectric layer 26. Specifically, the lateral attenuation length of the electric field at the edge of the microbridge contacts 27 is approximately 0.3 μm, and the overlap of the electric field between adjacent microbridge contacts 27 is greater than 99%, thereby ensuring that the piezoelectric layer 26 as a whole exhibits equivalent continuous capacitance characteristics.

[0099] It should be noted that although the microbridge contacts 27 are discretely distributed (5 μm in diameter, 2 mm in-plane spacing), since the in-plane spacing is much smaller than the electromagnetic wavelength corresponding to the target resonant frequency, each microbridge contact 27 couples to form a quasi-continuous equivalent distributed top electrode on the upper surface of the piezoelectric layer 26 through the electric field edge effect, thereby making the piezoelectric layer 26 exhibit an equivalent capacitance Cp as a whole. As an alternative, a continuous ITO transparent conductive layer (10 nm thick) or an ultrathin Au layer (5 nm thick) can be sputtered and deposited on the entire upper surface of the ZnO piezoelectric layer 26 as a second electrode, and then led out through the microbridge contacts 27 and the voice coil trace 31.

[0100] Using a precision LCR meter under 1 kHz testing conditions, the inherent inductance L of the voice coil trace 31 was measured to be 2.05 μH, and the equivalent capacitance Cp of the piezoelectric layer 26 was 156 pF. The resonant frequency f0 was calculated to be 8.91 kHz using the formula f0 = 1 / (2π sqrt(L·Cp)), which corresponds to the target split vibration frequency (approximately 9 kHz) of the diaphragm 2.

[0101] The impedance-frequency curve of the passive parallel resonant shunt circuit was measured using an impedance analyzer. A significant parallel resonant impedance peak appeared at 8.91 kHz, which is consistent with the theoretical calculation. The out-of-plane vibration displacement of the central region of diaphragm 2 was measured using a laser Doppler vibration meter (LDV) under sinusoidal excitation at 8.91 kHz. The vibration displacement amplitude in this embodiment was 0.38 μm, while the vibration displacement amplitude in Comparative Example 1 described later under the same conditions was 1.35 μm, resulting in a vibration suppression amplitude of 71.9%.

[0102] The sound pressure frequency response was tested in the IEC 60318-4 coupling cavity. In this embodiment, the sound pressure fluctuation in the 8 kHz–10 kHz frequency band was reduced from ±3.5 dB in Comparative Example 1 to ±0.7 dB, which proves that the piezoelectric shunt damping effectively suppressed the target segmented vibration mode.

[0103] Example 3: Local Reinforcement of Magnetorheological Elastomer Micro-Islands

[0104] See Figure 5 This embodiment provides a planar speaker unit with localized enhancement by magnetorheological elastomer micro-islands. The heterogeneous layer assembly further includes magnetorheological elastomer micro-islands 32, which are discretely distributed in the trace gap region of the voice coil trace 31. Under the action of the horizontal static magnetic field generated by the bar permanent magnet array in the outer magnetic circuit 1 and the inner magnetic circuit 4, the in-plane shear modulus of the magnetorheological elastomer micro-islands 32 is increased by more than 10 times compared with the zero magnetic field state, and the distribution area of ​​the magnetorheological elastomer micro-islands 32 coincides with the magnet gap region of the bar permanent magnet array in the in-plane projection.

[0105] The preparation method is as follows:

[0106] Step 1, Substrate and Voice Coil Preparation: Same as Step 1 and Step 2 of Example 1, prepare a polyimide diaphragm substrate layer 20 with serpentine Cu voice coil traces 31.

[0107] Step 2, surface modification: The magnet side surface of the diaphragm 2 is treated with oxygen plasma with the following parameters: power 100 W, O2 flow rate 50 sccm, time 180 s; then immediately immersed in 1 wt% 3-aminopropyltriethoxysilane anhydrous ethanol solution and reacted at room temperature for 30 min; rinsed with deionized water and dried with N2 to form a silanized monolayer on the polyimide surface.

[0108] Step 3, preparation of magnetorheological elastomer ink: using polydimethylsiloxane prepolymer Sylgard 184 (component A to component B mass ratio 10:1) as the matrix, incorporating 28% by volume carbonyl iron powder (BASF Carbonyl Iron PowderOM, particle size 3 μm~5 μm, surface passivated with phosphoric acid); adding 2 wt% fumed silica Aerosil 200 as a thixotropic agent; grinding three times with a 25 μm roller gap using a three-roll mill; adjusting the viscosity to 1000 cP with xylene dilution.

[0109] Step 4, Micro-inkjet printing: Using a piezoelectric inkjet printhead (nozzle diameter 50 μm, driving voltage 30 V, pulse width 8 μs), the magnetorheological elastomer ink is printed onto the gap area of ​​the voice coil trace 31. The printing path is aligned using a visual alignment system with the Cu serpentine trace as a reference, covering only the in-plane projection area of ​​the magnet gap area of ​​the strip permanent magnet array on the surface of the diaphragm 2. The volume of a single droplet is approximately 25 pL, with a landing accuracy of ±5 μm. After printing, the droplets spread under surface tension to form flat micro-islands with an in-plane equivalent diameter of approximately 40 μm and a thickness of approximately 80 nm. The center-to-center distance between adjacent micro-islands is 150 μm, and they are arranged in a hexagonal close-packed distribution.

[0110] Before assembling the magnetic circuit, the arrangement coordinates of the bar permanent magnets in the outer magnetic circuit 1 and the inner magnetic circuit 4 are determined by three-dimensional optical scanning to determine the projected boundary of the magnet gap region on the mounting plane of the diaphragm 2. The width of the magnet gap region is determined by the magnetic circuit design parameters, and the coordinate data of its projected boundary relative to the central axis of the magnetic circuit is imported into the visual alignment system of the inkjet printer.

[0111] Two 1 mm diameter positioning holes are pre-punched at the edge of the substrate layer 20, with a center-to-center distance of 50 mm. Positioning pins are set at corresponding positions on the magnetic circuit support. During printing, using the Cu serpentine voice coil trace 31 as a visual reference, and combining the mechanical limiting of the positioning holes and positioning pins, the coordinate system of the printing path is aligned with the coordinate system of the magnet gap projection. The visual alignment system identifies the straight line segments of the voice coil trace 31, calculates its relative offset (Δx, Δy) from the magnet gap projection boundary, and compensates for it through the closed-loop displacement stage of the piezoelectric inkjet printhead, achieving a registration accuracy better than ±5 μm. After printing, random inspection using an optical microscope shows that the in-plane deviation between the center of the magnetorheological elastomer micro-island 32 and the center of the magnet gap region is less than 8 μm.

[0112] Step 5, Curing: Place the printed diaphragm 2 on an 80°C hot plate for 45 min to cure, so that the polydimethylsiloxane body completes the crosslinking reaction; no external magnetic field is applied during the curing process to maintain the isotropic distribution of the carbonyl iron powder in the micro-island.

[0113] Step 6, magnetic field activation: The cured diaphragm 2 is installed into the outer magnetic circuit 1 and the inner magnetic circuit 4. The strip permanent magnet is an NdFeB permanent magnet with a surface magnetic field strength of 1.0 T. The carbonyl iron powder forms a chain-like aggregate structure along the magnetic field direction under the action of the horizontal static magnetic field.

[0114] SEM observation revealed that the magnetorheological elastomer micro-islands 32 are hexagonally close-packed within the trace gaps of the voice coil traces 31, with an in-plane equivalent diameter of 38 μm to 42 μm and a thickness of 75 nm to 85 nm. Dynamic mechanical analyzer (DMA) testing at 1 kHz in shear mode showed that the in-plane shear modulus of the micro-islands was 1.6 MPa in zero magnetic field condition; under a 1.0 T horizontal static magnetic field, the in-plane shear modulus of the micro-islands increased to 28.5 MPa, an increase of approximately 17.8 times.

[0115] This embodiment was assembled in the audio magnetic circuit, and the sound pressure frequency response was tested under magnetic field conditions of 0 T, 0.5 T, and 1.0 T. The results show that under 1.0 T (normal operating magnetic field), the sound pressure fluctuation in the 10 kHz–20 kHz frequency band decreased from ±4.0 dB at 0 T to ±1.3 dB, proving that the magnetorheological elastomer micro-island 32 effectively improved the local stiffness of the diaphragm 2 in the audio working magnetic field and suppressed high-frequency split vibration.

[0116] Example 4: Surface modulus gradient layer for voice coil traces

[0117] See Figure 6 This embodiment provides a modulus gradient layer on the surface of the voice coil trace. The heterogeneous layer group further includes a modulus gradient sublayer covering at least a portion of the trace surface of the voice coil trace 31. The Young's modulus of the modulus gradient sublayer is different from the Young's modulus of the main material of the voice coil trace 31, and the modulus gradient sublayer is non-uniformly distributed in the plane of the diaphragm 2.

[0118] The preparation method is as follows:

[0119] Step 1, Substrate and Voice Coil Preparation: Same as Step 1 and Step 2 of Example 1, prepare a polyimide substrate layer 20 with a thickness of 2.0 μm and a serpentine Cu voice coil trace 31 with a thickness of 100 nm. The line width of the voice coil trace 31 is 30 μm and the line spacing is 90 μm.

[0120] Step 2, selective masking: spin-coat positive photoresist AZ 1512 to a thickness of 1.5 μm on the surface of the voice coil trace 31; through overlay exposure, only the surface of the trace segment in the central region with a radius r < 15 mm is exposed, while the surface of the trace segment in the edge region with a radius r > 40 mm is covered and protected by the photoresist; the exposure alignment accuracy is better than 2 μm.

[0121] Step 3, selective electroplating of Ni-W alloy: The exposed diaphragm 2 is immersed in a nickel sulfamate-tungstate electroplating solution, the composition of which is: 200 g / L nickel sulfamate, 30 g / L sodium tungstate, 40 g / L citric acid, 10 g / L nickel chloride, pH 3.5, temperature 45°C; the Cu voice coil trace 31 is used as the cathode, the insoluble anode, and the current density is 1 A / dm³. 2 Electroplating time 5 min, depositing Ni-W amorphous alloy nanolayer 29 with a thickness of 30 nm on the exposed central region trace surface; the atomic fraction of W in the Ni-W alloy is 30%.

[0122] Step 4, Resin Removal and Cleaning: Use acetone for ultrasonic removal for 3 minutes to remove the photoresist covering the trace surface of the edge area, exposing the original Cu trace surface; rinse with deionized water and dry with N2.

[0123] Step 5, post-processing: The entire surface of the diaphragm 2 is cleaned with oxygen plasma to remove residual adhesive; a 5 nm thick parylene C protective layer 24 is sprayed using chemical vapor deposition.

[0124] SEM / EDS analysis revealed that the voice coil trace 31 in the central region (r < 15 mm) is uniformly covered with the Ni-W alloy nanolayer 29, with a thickness of 29 nm to 31 nm and a W atomic fraction of 30.2%. The equivalent bending stiffness of the composite structure of the voice coil trace 31 and substrate layer 20 in the central region, tested using a nanoindenter, was 2.48 times higher than that in the edge region (exposed Cu traces). Nano-scratch testing showed that the Vickers hardness of the Ni-W alloy nanolayer 29 was 645 HV, significantly higher than the 120 HV of Cu.

[0125] The areal density increment was measured using a precision balance: the areal density increment of the Ni-W alloy nanolayer 29 was 0.00039 g / cm³. 2 The total mass of the diaphragm 2 increases by 1.7%.

[0126] The sound pressure frequency response was tested in an IEC 60318-4 coupling cavity. Compared to Comparative Example 1, the high-frequency split vibration onset frequency of this embodiment was delayed from 6.5 kHz to 8.6 kHz, a delay of approximately 2.1 kHz, and the sound pressure fluctuation in the 10 kHz–15 kHz frequency band was reduced from ±5.5 dB to ±1.8 dB. Simultaneously, after an aging test at 85°C / 85% RH for 240 h, the DC resistance change rate of the voice coil trace 31 in the central region was <0.5%, demonstrating that the Ni-W alloy nanolayer 29 significantly improved the trace's anti-electromigration performance.

[0127] Example 5: Radial modulus gradient of ion-implanted modified substrate

[0128] See Figure 2 This embodiment provides an ion-implanted modified substrate. The substrate layer 20 is a polyimide film modified by Si⁺ ion implantation, wherein the ion implantation dose in the central region (radius r < 15 mm) is higher than that in the edge region (radius r > 40 mm), resulting in a Young's modulus in the central region being 35% higher than that in the edge region.

[0129] The preparation method is as follows:

[0130] Step 1, Substrate preparation: Select a 2.0 μm thick polyimide film as the original substrate.

[0131] Step 2, Design and Installation of the Movable Mask: A 200 μm thick stainless steel mask is used, with radially tapered slits. The width of the slits varies continuously radially: 2.0 mm in the central region (r < 15 mm), 0.3 mm in the edge region (r > 40 mm), and in the intermediate region (15 mm ≤ r ≤ 40 mm), the slit width continuously and gradually changes according to a linear function w(r) = 2.0 - 0.0486 × (r - 15) mm. The mask is mounted on the sample holder of the electric rotary table, and the original substrate is fixed below the mask, with a distance of 50 μm between them.

[0132] Step 3, Ion implantation dose gradient formation: using Si + The original substrate was irradiated with an ion beam at an ion energy of 100 keV and a beam current density of 5 μA / cm. 2 During the injection process, the electric rotary stage rotates at a constant speed of 0.5 rpm, while the sample holder translates radially from the center to the outer edge at a speed of 0.1 mm / s, forming a helical scanning trajectory. By controlling the coupling of the rotational speed and the radial translational speed, the cumulative injection dose in the central region (r < 15 mm) reaches 1 × 10⁻⁶. 15 ions / cm 2 The cumulative injection dose in the marginal region (r>40 mm) is 3×10⁻⁶. 14 ions / cm 2 The intermediate region exhibits a continuous gradient transition. During the injection process, the back side of the original substrate is cooled with helium to maintain a temperature below 80°C. After injection, the dosage of each region is verified using a Faraday cup, with the error controlled within ±5%.

[0133] Step 4, post-treatment: After ion implantation, the substrate surface is cleaned with deionized water to remove sputtered deposits; annealing is performed at 150°C for 30 min to allow the free radicals generated by irradiation to fully react and stabilize.

[0134] Step 5, voice coil fabrication: On the surface of the substrate layer 20 after ion implantation modification, a serpentine Cu voice coil trace 31 is fabricated using the same process as in Example 1.

[0135] Nanoindentation testing revealed that the Young's modulus of the central region (at r=10 mm) was 4.2 GPa, and the Young's modulus of the edge region (at r=45 mm) was 3.1 GPa, exhibiting a continuous gradient change in the middle region. The total thickness of the substrate layer 20 remained at 2.0 μm, with an elongation at break of 32%.

[0136] Example 6: Modal Splitting of Asymmetric Biaxially Oriented Substrates

[0137] See Figure 2This embodiment provides an asymmetric biaxially oriented substrate. The substrate layer 20 is a biaxially stretched polyimide film with in-plane anisotropy, and its longitudinal (first direction) Young's modulus E MD ≈3.8 GPa, Young's modulus E in the transverse (second direction) TD ≈2.9 GPa, ratio E MD / E TD ≈1.31. The first direction forms a 45° angle with the extension direction of the straight segment of the serpentine routing of the voice coil trace 31.

[0138] The preparation and alignment methods are as follows:

[0139] Step 1: Preparation of asymmetric biaxially oriented polyimide film: A polyamic acid precursor solution (15 wt% solids content, N,N-dimethylacetamide as solvent) is extruded through a slit die onto a stainless steel strip to form a wet film with a thickness of 200 μm. The film is then dried at 80°C for 10 min to remove some of the solvent. The wet film is fed into a biaxial stretching machine, where it is first stretched longitudinally at 120°C with a stretch ratio of 3.5; subsequently stretched transversely at 130°C with a stretch ratio of 2.7; the longitudinal to transverse stretching speed ratio is 1.2:1. Immediately after stretching, the film is heat-set at 280°C for 60 s to imidize the polyamic acid, yielding an asymmetric biaxially oriented polyimide film.

[0140] Step 2, alignment mark prefabrication: Two sets of cross alignment marks are prefabricated in the edge region of the film by ultraviolet laser ablation. The mark line width is 50 μm and the length is 1 mm. One arm of the cross mark is parallel to the longitudinal direction (high modulus direction), and the other arm is parallel to the transverse direction (low modulus direction).

[0141] Step 3, Orientation Alignment and Cutting: The film is placed on the vacuum adsorption rotary table of the laser cutting machine, and the crosshair alignment mark is identified by the CCD vision alignment system. The table is rotated so that the angle between the longitudinal high modulus direction and the extension direction of the straight segment of the serpentine routing of the voice coil trace 31 is 45°±1°. After the angle is confirmed, a circular diaphragm with a diameter of 60 mm is cut out using an ultraviolet laser (wavelength 355 nm, power 5 W). The angle error is controlled within ±1°; if the angle deviation exceeds ±2°, the sub-mode frequency difference Δf after the (m,n) mode split will deviate from the design value by more than 15%, resulting in a significant deterioration in the diffusion effect of axial sound pressure radiation.

[0142] Step 4, voice coil fabrication: a serpentine Cu voice coil trace 31 is fabricated on the surface of the substrate layer 20, wherein the angle between the extension direction of the straight segment of the trace and the longitudinal high modulus direction is 45°.

[0143] Laser Doppler vibration measurement showed that the (2,1) axisymmetric bending mode of the diaphragm split into two sub-modes with frequencies of 8.2 kHz and 9.1 kHz, respectively, and a frequency difference Δf = 0.9 kHz, which is consistent with the theoretically predicted value Δf ∝ sqrt(E MD / E TD They are basically consistent.

[0144] Comparative Example 1

[0145] The same 2.0 μm polyimide substrate layer 20 and Cu voice coil trace 31 as in Example 1 were used, but no heterogeneous layer groups were set (i.e., no high-mode quantum layer 21, low-mode quantum layer 23, piezoelectric layer 26, magnetorheological elastomer micro-islands 32, and Ni-W alloy nanolayer 29 were present), and only a 5 nm parylene C protective layer 24 was sprayed on. This comparative example served as a benchmark sample for performance comparison with Examples 1–4 above.

[0146] Comparative Example 2

[0147] The same preparation method as in Example 1 was used, but only the SiO2 nanolayer was filled as a high-mode quantum layer 21 in the central region (r < 12 mm) of the trace gaps. No low-mode quantum layer 23 or intermediate transition region 22 was provided in the edge region. Testing showed that although high-frequency breakover vibration was somewhat suppressed, the lack of low-mode buffering in the edge region resulted in a 2.1 dB reduction in the 100 Hz low-frequency sound pressure level compared to Comparative Example 1, leading to a tighter sound. This comparative example demonstrates that a single high-mode quantum layer cannot simultaneously achieve low-frequency compliance and high-frequency breakover vibration suppression.

[0148] Thus far, the description of the above embodiments has been provided for illustrative and descriptive purposes. This is not intended to be exhaustive or limiting of the present disclosure. Individual elements or features of particular embodiments are generally not limited to those particular embodiments, but may be interchanged and used in selected embodiments where applicable, even if not specifically shown or described. In many respects, the same elements or features may also be varied. Such variations are not considered a departure from this disclosure, and all such modifications are intended to be included within the scope of this disclosure.

[0149] Example embodiments are provided so that this disclosure will become thorough and will fully convey the scope to those skilled in the art. Numerous details, such as examples of specific parts, apparatus, and methods, are set forth to provide a thorough understanding of embodiments of this disclosure. It will be apparent to those skilled in the art that the specific details are not required, and the example embodiments may be implemented in many different forms, neither of which should be construed as limiting the scope of this disclosure. In some example embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

[0150] Technical terms are used herein for the purpose of describing specific exemplary embodiments only and are not intended to be limiting. Unless the context clearly indicates otherwise, the singular forms “a” and “the” as used herein may also refer to the plural forms. The terms “comprising” and “having” mean inclusive and therefore specify the presence of the stated features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or additional having of one or more other features, integrals, steps, operations, elements, components, and / or combinations thereof. Unless expressly indicated in order of execution, the method steps, processes, and operations described herein are not to be construed as necessarily requiring performance in the specific order discussed and shown. It should also be understood that additional or optional steps may be employed.

Claims

1. A planar speaker unit with a multilayer heterogeneous composite diaphragm, comprising a diaphragm, a planar voice coil disposed on at least one surface of the diaphragm, and a strip permanent magnet array located on both sides of the diaphragm and cooperating with the planar voice coil, characterized in that: The diaphragm includes a substrate layer and a heterogeneous layer group. The heterogeneous layer group includes at least two types of heterogeneous sublayers respectively disposed in different regions within the plane of the diaphragm. The at least two types of heterogeneous sublayers have different Young's moduli, and at least a portion of the heterogeneous sublayers are disposed in the trace gap region of the planar voice coil or cover at least a portion of the trace segment surface of the planar voice coil.

2. The flat panel speaker unit according to claim 1, characterized in that: The at least two heterolayers include a high-mode quantum layer located in the central region of the diaphragm and a low-mode quantum layer located in the edge region of the diaphragm. The Young's modulus of the high-mode quantum layer is greater than 10 GPa, the Young's modulus of the low-mode quantum layer is less than 1 GPa, and an intermediate transition region without heterolayers is formed between the high-mode quantum layer and the low-mode quantum layer.

3. The flat panel speaker unit according to claim 2, characterized in that: The high-mode quantum layer is an inorganic oxide nanolayer formed in the wiring gap region by sputtering or atomic layer deposition, and the low-mode quantum layer is a viscoelastic polymer nanolayer formed in the wiring gap region by spin coating or inkjet printing.

4. The flat panel speaker unit according to claim 3, characterized in that: The inorganic oxide nanolayer is SiO2 or Al2O3 with a thickness of 30 nm to 100 nm; the viscoelastic polymer nanolayer is fluorosilicone rubber, polyurethane acrylate or polydimethylsiloxane derivative with a thickness of 30 nm to 100 nm.

5. The flat panel speaker unit according to claim 1, characterized in that: The diaphragm further includes a piezoelectric layer and piezoelectric electrodes. The piezoelectric layer is located between the substrate layer and the planar voice coil. The piezoelectric electrodes include a first electrode and a second electrode. The first electrode is disposed on the side of the piezoelectric layer closer to the substrate layer. The second electrode is electrically connected to at least a portion of the traces of the planar voice coil through microbridge contacts distributed in the trace gap region of the planar voice coil, so that the inherent inductance of the piezoelectric layer and at least a portion of the traces of the planar voice coil constitutes a passive parallel resonant shunt circuit. The first electrode is connected to the other end of the voice coil trace via a lead-out electrode through the trace gap, or the first electrode is connected to the common terminal of the voice coil and grounded.

6. The flat panel speaker unit according to claim 5, characterized in that: The piezoelectric layer is a c-axis preferred-oriented ZnO thin film deposited by sputtering, with a thickness of 50 nm to 150 nm; the diameter of the microbridge contact is 3 μm to 10 μm, and the in-plane spacing is 1 mm to 5 mm; the resonant frequency of the passive parallel resonant shunt circuit corresponds to the target segmented vibration frequency of the diaphragm.

7. The flat panel speaker unit according to claim 1, characterized in that: The heterogeneous layer group further includes a modulus gradient sublayer covering at least a portion of the trace surface of the planar voice coil. The Young's modulus of the modulus gradient sublayer is different from the Young's modulus of the main material of the planar voice coil, and the modulus gradient sublayer is non-uniformly distributed in the plane of the diaphragm.

8. The flat panel speaker unit according to claim 7, characterized in that: The main material of the planar voice coil is Cu, and the modulus gradient sublayer is a Ni-W alloy nanolayer formed by selective electroplating with a thickness of 20 nm to 50 nm.

9. The flat panel speaker unit according to claim 1, characterized in that: The heterostructure also includes magnetorheological elastomer micro-islands, which are discretely distributed in the trace gap region of the planar voice coil. The thickness of the magnetorheological elastomer micro-islands is 50 nm to 100 nm, and the in-plane equivalent diameter is 30 μm to 60 μm.

10. The flat panel speaker unit according to claim 9, characterized in that: Under the action of the horizontal static magnetic field generated by the strip permanent magnet array, the in-plane shear modulus of the magnetorheological elastomer micro-island is increased by more than 10 times compared with the zero magnetic field state, and the distribution area of ​​the magnetorheological elastomer micro-island coincides with the magnet gap area of ​​the strip permanent magnet array on the in-plane projection.

Images