MEMS micro loudspeaker packaging structure and preparation method thereof

Abstract

The invention relates to the technical field of semiconductors, in particular to an MEMS micro loudspeaker packaging structure and a preparation method thereof, and the packaging structure comprises a substrate which is provided with a hollow cavity structure, a limiting device and a plurality of vent holes in the bottom; and the MEMS sound production chip is inversely arranged on the substrate, and the edge area of the MEMS sound production chip is bonded with the substrate through the connecting part. According to the packaging structure of the MEMS micro loudspeaker provided by the invention, the MEMS sound production chip is inversely arranged and is in direct contact with the substrate used for packaging, so that the packaging structure has higher impact resistance, the inversely arranged MEMS sound production chip can better dissipate heat, and a double-sound-cavity structure in the packaging structure increases system damping and reduces the quality factor of device resonance; the stability and reliability of the chip can be improved, the design of multiple vent holes is combined with the limiting device, the nonlinear displacement of the MEMS sound production chip under the resonant frequency is effectively inhibited, and the total harmonic distortion is reduced.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to a MEMS micro-speaker packaging structure and a preparation method thereof. Background Art

[0002] Traditional dynamic speakers are large, manual or semi-automatic, and relatively expensive. The use of MEMS micro-electromechanical system manufacturing technology based on thin film materials can effectively reduce the size of the MEMS sound chip and enable mass production to reduce costs. Since the MEMS sound chip is small in size, thin in thickness, and its structure cannot be directly exposed to the external environment, a packaging structure is required to protect the MEMS sound chip, achieve fully automated assembly, and form a system with multifunctional MEMS micro-acoustics. The packaged device has a small size and thin appearance, can withstand SMT 260℃ reflow soldering, and can be soldered on the PCB, thereby reducing the complexity and cost of system integration. In the application of in-ear headphone products, it only requires very small space and weight.

[0003] In traditional MEMS chip packaging technology, MEMS speakers are packaged with components such as a MEMS sound chip, a metal housing, and a substrate, and the electrical connection between the substrate and the MEMS sound chip PAD is achieved through metal leads. This method usually increases the package volume, has low reliability, and is difficult to improve the acoustic performance of the MEMS speaker after packaging. In addition, the quality factor (Q factor) of the resonance of the MEMS sound chip made of silicon film and piezoelectric film is usually 100±40. When the voltage drive signal frequency is consistent with the resonant frequency of the MEMS sound chip, the diaphragm resonance will produce a serious offset and cause considerable nonlinearity, resulting in a narrow peak in the displacement frequency response curve and a high peak value. This leads to the total harmonic distortion (THD) of the MEMS speaker. The larger the THD, the worse the sound quality. Summary of the Invention

[0004] In view of this, an object of the present invention is to provide a MEMS micro-speaker packaging structure and a manufacturing method thereof.

[0005] In a first aspect, an embodiment of the present invention provides a MEMS micro-speaker packaging structure, the packaging structure comprising: The base plate has a hollow cavity structure, a limiting device, and multiple ventilation holes at the bottom; The MEMS sound chip is mounted upside down on the substrate, with its edge area bonded to the substrate through a joint. The MEMS sound chip diaphragm can vibrate up and down relative to the substrate along the lifting axis; The packaging cap covers the MEMS sound chip, has an opening on its upper surface, and its bottoms on both sides are connected to the substrate. It surrounds the outer edge of the MEMS sound chip substrate, and its lower middle surface is connected to the lower surface of the substrate; The dual-acoustic cavity structure includes an upper acoustic cavity and a lower acoustic cavity. The upper acoustic cavity is formed by the MEMS sound chip and the packaging cap; the lower acoustic cavity is surrounded by the MEMS sound chip and the substrate and is connected to the external environment through a vent. Microporous film elements cover the vent holes of the substrate to achieve dust and water resistance and air pressure balance; Among them, the MEMS sound chip is equipped with a cavity and multiple through holes inside. The size of the through holes is much smaller than the size of the cavity. The sound waves propagate toward the upper sound cavity through the cavity and through holes.

[0006] In combination with the first aspect, the MEMS sound chip includes at least a substrate, a piezoelectric composite unit, a diaphragm and an electrode PAD; the material of the piezoelectric composite unit is selected from at least one of single crystal AlN, doped AlN, PZT, and ZnO, and the thickness is 0.25~10um.

[0007] In combination with the first aspect, a limiting unit is provided in the MEMS sound chip to limit the displacement amplitude of the diaphragm at the resonant frequency.

[0008] In combination with the first aspect, the packaging cap is made of metal or ceramic, and its openings are arranged in a circular, square or polygonal array, and the openings are located close to the effective vibration area of ​​the diaphragm.

[0009] In combination with the first aspect, there are multiple openings, and the multiple openings are arranged in an array. In combination with the first aspect, an insulating layer is further provided on a side of the piezoelectric composite unit close to the substrate.

[0010] In combination with the first aspect, an adhesive layer is provided between the packaging cap and the substrate.

[0011] In a second aspect, an embodiment of the present application further provides a method for preparing a MEMS micro-speaker packaging structure, comprising: Provide MEMS wafers and substrates; Back grinding, laser grooving and dicing of MEMS wafers into independent MEMS sound chips; Flip-chip solder the MEMS sound chip to the substrate, and fill the bottom of the MEMS sound chip with non-conductive glue to fix and seal the solder joints; Solder paste is placed on the surface of the substrate, and a packaging cap with an acoustic opening is installed to wrap the MEMS sound chip.

[0012] In conjunction with the second aspect, before the step of providing the MEMS wafer and the substrate, the method further includes: Performing RIE etching on the pre-treated substrate to obtain a groove of a specified size; Filling the groove with a sacrificial layer and polishing the substrate surface to make it smooth and flat; growing barrier layers on the front and back sides of the substrate, and generating support and functional layers on the front side; Patterning and etching the piezoelectric layer and the electrode layer; Deposit and pattern the passivation layer, and form metal traces and pads through a lift-off process; Vacuum lamination of flexible dry film and photolithography patterning; The substrate is thinned and a cavity is formed on the back side of the substrate by DRIE etching; The sacrificial layer and the oxide layer are removed to form a cavity structure, thereby obtaining a MEMS wafer.

[0013] In combination with the second aspect, the size of the cavity of the substrate is larger than the size of the diaphragm in the MEMS sound chip, and the depth of the cavity is larger than the maximum offset of the diaphragm.

[0014] The embodiments of the present invention bring the following beneficial effects: A MEMS micro-speaker packaging structure provided by the present application includes: a substrate having a hollow cavity structure, a limit device and multiple air vents at the bottom; a MEMS sound chip, which is mounted upside down on the substrate, with its edge area bonded to the substrate through a connection, and can vibrate up and down relative to the substrate along the lifting axis; a packaging cap, which covers the top of the MEMS sound chip, has an opening on its upper surface, and its bottoms on both sides are connected to the substrate, surrounding the outer edge of the MEMS sound chip substrate, and the middle lower surface is connected to the lower surface of the substrate; a dual-acoustic cavity structure, including an upper acoustic cavity and a lower acoustic cavity, the upper acoustic cavity is formed by the MEMS sound chip and the packaging cap; the lower acoustic cavity is surrounded by the MEMS sound chip and the substrate, and is connected to the external environment through the air vents; a microporous film element, which covers the air vents of the substrate to achieve dustproof and waterproof and air pressure balance; wherein, a cavity and multiple through holes are provided inside the MEMS sound chip, the size of the through holes is much smaller than the size of the cavity, and sound waves propagate to the upper acoustic cavity through the cavity and the through holes.

[0015] The MEMS micro-speaker packaging structure provided by this application has higher impact resistance by flipping the MEMS sound chip and directly contacting it with the packaging substrate. The flipped MEMS sound chip can better dissipate heat. The dual acoustic cavity structure in the packaging structure increases system damping, reduces the quality factor of the device resonance, and can improve the stability and reliability of the chip. The chip cavity and multi-vent design combined with a limit device effectively suppress the nonlinear displacement of the MEMS sound chip at the resonant frequency, reduce the THD of the overall sound system, and improve the sound quality of the sounder. At the same time, the flip-chip stacking method simplifies the packaging process, can effectively reduce the volume of the MEMS speaker after packaging, and is dust-proof and waterproof, improving the reliability of the device.

[0016] Other features and advantages of the present invention will be described in the following description, and in part will become apparent from the description, or understood by practicing the present invention. The purposes and other advantages of the present invention are realized and obtained by the structures particularly pointed out in the description, claims and drawings.

[0017] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, preferred embodiments are given below and described in detail with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 A schematic diagram of a MEMS micro-speaker packaging structure provided by an embodiment of the present invention; Figure 2 A front view schematic diagram of the MEMS sound chip D01 provided in an embodiment of the present invention; Figure 3 for Figure 2 A cross-sectional view of the provided MEMS sound chip D01; Figure 4 A schematic diagram of the structure of the MEMS micro-speaker packaging structure provided by an embodiment of the present invention with the opening located on the right side; Figure 5 A schematic diagram of the structure of the MEMS micro-speaker packaging structure provided by an embodiment of the present invention with the opening located on the left side; Figure 6 A schematic diagram of the structure of the MEMS micro-speaker packaging structure provided by an embodiment of the present invention, wherein the packaging cap is connected to the MEMS sound chip D01 via an adhesive layer; Figure 7 A schematic diagram of the structure of the MEMS micro-speaker packaging structure provided by an embodiment of the present invention having multiple openings arranged at intervals; Figure 8 A schematic flow chart of a method for preparing a MEMS micro-speaker packaging structure according to an embodiment of the present invention; Figure 9 The figure shows the test results of the acoustic performance test of MEMS micro speakers with different packaging forms; Figure 10 A schematic diagram of the structure of etching a chip substrate to obtain a groove; Figure 11 To pass through the sacrificial layer Figure 10 Schematic diagram of the structure after the groove is filled and leveled.

[0020] Reference numerals: 01-substrate, 02-through hole, 03-limiting unit, 04-chip cavity, 05-oxide layer, 06-conductive PAD, 07-insulating layer, 08-dry film, 09-piezoelectric composite unit; 11 - packaging cap, 12 - opening, 13 - upper acoustic cavity, 14 - bonding layer, 15 - connection, 16 - substrate electrical PAD, 17 - soldering pad, 18 - limit device, 19 - lower acoustic cavity; 21-vent, 22-microporous film element, 23-substrate. DETAILED DESCRIPTION

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work shall fall within the scope of protection of the present invention.

[0022] To facilitate understanding of this embodiment, the following is a brief introduction to the technical terms used in this application.

[0023] THD (Total Harmonic Distortion) is the ratio of the harmonic components of the original signal (such as harmonics at twice, three times, etc. the frequency) to the original fundamental wave. It is usually expressed as a percentage (%). It is a parameter that measures the degree of harmonic distortion caused by nonlinear characteristics when an audio device or system reproduces the sound signal.

[0024] After introducing the technical terms involved in this application, the application scenarios and design concepts of the embodiments of this application are briefly introduced.

[0025] Traditional MEMS speaker packaging is large and has low reliability. In addition, because the Q factor (quality factor) of the MEMS sound chip is large (about 100±40), the diaphragm is severely offset at the resonant frequency and the nonlinear distortion is large, causing the total harmonic distortion (THD) to be too high, seriously affecting the sound quality.

[0026] Based on this, an embodiment of the present application provides a MEMS micro-speaker packaging structure and a preparation method thereof.

[0027] Example 1 The present application provides a MEMS micro speaker packaging structure, combined with Figure 1As shown, it includes: a substrate 23, a MEMS sound chip D01, a packaging cap 11, a dual-acoustic cavity structure and a microporous film element 22.

[0028] The base plate 23 has a hollowed-out cavity structure, a limiting device 18 and a plurality of ventilation holes 21 at the bottom.

[0029] The MEMS sound chip is mounted upside down on the substrate 23 , with its edge region bonded to the substrate 23 via a connection 15 . The diaphragm of the MEMS sound chip can vibrate up and down relative to the substrate 23 along the lifting axis.

[0030] The packaging cap 11 covers the MEMS sound chip, has an opening 12 on its upper surface, and is connected to the base plate 23 at both sides of the bottom, surrounding the outer edge of the MEMS sound chip substrate.

[0031] The dual-acoustic cavity structure includes an upper acoustic cavity 13 and a lower acoustic cavity 19. The upper acoustic cavity 13 is formed by the MEMS sound chip cavity 04, the through hole 02 and the packaging cap 11; the lower acoustic cavity 19 is surrounded by the MEMS sound chip diaphragm and the substrate 23, and is connected to the external environment through the vent 21.

[0032] The microporous film element 22 covers the vent holes 21 of the substrate 23 to achieve dustproof and waterproof properties and air pressure balance.

[0033] Among them, the MEMS sound chip substrate forms a chip cavity 04 and multiple through holes 02 through the MEMS process. The size of the through hole 02 is much smaller than the size of the chip cavity 04. The sound waves propagate toward the upper sound cavity 13 through the chip cavity 04 and the through holes 02.

[0034] The present invention provides a packaging structure for a MEMS acoustic wave device. By combining an inverted MEMS sound-generating chip with a substrate 23, a compact dual-cavity structure (upper and lower cavities) is formed, enabling miniaturization of the device and optimizing acoustic performance. Within the packaging structure, the multi-vent design 21, combined with a stopper 18, effectively suppresses the nonlinear displacement of the MEMS sound-generating chip at the resonant frequency, reduces total harmonic distortion (THD), and enhances audio fidelity. Simultaneously, a microporous film element 22 covers the substrate vents 21, providing both dust and water resistance and air pressure balance, thereby improving the device's reliability and stability in complex environments. Furthermore, the flip-chip stacking method simplifies the packaging process, improves production efficiency, and effectively reduces size, enhancing the device's environmental adaptability and wide range of application scenarios.

[0035] Substrate 23 can be made of materials such as RF4, BT, ceramic, or silicon, with a thickness ranging from 0.1mm to 0.8mm. Electrode connection points for the MEMS chip are provided on substrate 23. These points can be electrically connected to the conductive PAD06 of the MEMS sound chip through thermoacoustic or thermocompression welding, and then connected to the electrical welding area on the bottom of substrate 23 via circuit traces.

[0036] In this embodiment, the substrate 23 has a hollow cavity and at least one vent 21. The space formed by the hollow cavity and the MEMS sound chip is connected to the external environment through the vent 21. The rest of the space is enclosed. The depth of the hollow cavity is much greater than the maximum amplitude of the diaphragm in the MEMS generating unit, thus providing sufficient space for the diaphragm to vibrate up and down. The array of vents 21 on the substrate 23 changes the propagation path of sound waves, reduces reflective coupling, and increases the aperture to reduce the obstruction of air damping on the diaphragm, thereby improving the sound pressure level. It can be understood that the appropriate size and distribution of vents 21 can optimize the air flow path and further enhance the sound pressure level. Increasing the diameter of the vents 21 in the substrate 23 from 0.3mm to 0.5mm can improve acoustic impedance matching. At the same time, the viscous loss generated when the sound wave passes through the vents enhances air damping to suppress the nonlinear resonant displacement of the diaphragm, reducing the total harmonic distortion generated by the resonant frequency of the MEMS sound device. Increasing the substrate thickness from 0.5mm to 0.3mm can also help reduce bending stiffness.

[0037] In addition, positioning and installation position marks of the MEMS chip are set on the substrate 23, so that the MEMS chip can be accurately bonded to the substrate electrical PAD16 by flip-chip, and the gap between the MEMS chip and the substrate 23 is fixedly filled and sealed by filling glue on the substrate 23, thereby protecting the welding bumps and firmly connecting the MEMS chip without loosening.

[0038] In addition, the lower surface of the substrate 23 has a microporous film element 22, which is used to seal the vent holes 21 of the substrate 23 and tightly fit horizontally. The microporous film element 22 has an acoustic impedance of 48 MKS Rayls to 52 MKS Rayls, particularly 50 MKS Rayls, and a pore size of 34 μm to 38 μm, particularly 36 μm. The microporous film element 22 can be made of polytetrafluoroethylene (e-PTFE), a flexible and elastic microporous material. Polytetrafluoroethylene microporous material has a high porosity and uniform pore size distribution, is breathable, has a low coefficient of friction, and has minimal adsorption. It is not only dustproof, oleophobic, and hydrophobic, but also thermally stable, resistant to chemical media corrosion and UV resistance. It has a wide operating temperature range and can continuously perform its breathable function at temperatures between -40°C and 150°C. Furthermore, the waterproof and breathable membrane is bidirectionally water-resistant and breathable, eliminating fog and maintaining internal and external balance, while also providing waterproof and sound-permeable properties.

[0039] In combination with the first aspect, the MEMS sound chip includes at least a substrate 01, a piezoelectric composite unit 09, a diaphragm and a conductive PAD06; the material of the piezoelectric composite unit 09 is selected from at least one of single crystal AlN, doped AlN, PZT, and ZnO, with a thickness of 0.25~10um.

[0040] Combine Figure 2The schematic diagram of the structure of the MEM generating chip D01 is shown in FIG. Figure 3 The cross-sectional schematic diagram shows a MEMS piezoelectric sound chip D01. The dashed lines in areas 10a, 10b, 10c, and 10d represent the edges of the etched cavity on the back of the piezoelectric MEMS acoustic transducer. The four dashed lines form a square structure, which also marks the boundary of the device's vibrating membrane (diaphragm). A deep silicon etch process removes the silicon layer in the back cavity, creating a hollowed-out cubic cavity that forms the diaphragm structure of the MEMS acoustic transducer. Figures 40a and 40b represent the piezoelectric composite element 09 of the MEMS acoustic transducer. Figures 20a, 20b, 20c, and 20d represent gaps that extend to the edge of the chip's cavity 04 and extend beyond the center of 40a. The gaps divide 40a near the cavity edge, but 40a remains a single unit, with electrical conductivity identical from top to bottom. The D01 device features spring-slit structures (30a, 30b, 30c, and 30d) etched near the four inner boundaries of 40a. These spring structures can be S-shaped, semi-elliptical, or branch-shaped. Driven by a piezoelectric signal, the diaphragm of the MEMS piezoelectric sound unit D01 vibrates in a piston-like manner. The linear gaps (20a, 20b, 20c, and 20d) in the D01 device primarily relieve residual stress in the diaphragm, reducing the risk of stress-induced deformation or even rupture. They also decouple the device structure, enabling greater drive displacement and sound pressure level output. The MEMS device's first-order resonant frequency is designed to exceed 20kHz, and its piston-mode structure minimizes nonlinearity, resulting in no resonance within the audio signal band. Its ultrasonic characteristics ensure that the typical large nonlinear displacement of loudspeakers within the audible range is virtually eliminated. This ensures high-fidelity, distortion-free response and inherently low THD. The audio driving signal applied to 40a and 40b corresponds to the output sound wave signal. The audio driving signal is generally a sinusoidal signal of DC voltage plus AC voltage, such as DC 10V + AC 10Vp, or driven by a bipolar signal.

[0041] Combine Figure 3 The cross-sectional schematic diagram of the MEM sound generating chip D01 shown in FIG. 1 includes a substrate 01 , a diaphragm, and an actuator.

[0042] The chip cavity 04 is formed by removing silicon from the substrate 01 through a DRIE process. Substrate 01 has a bilaterally symmetrical structure and can be square, circular, rectangular, hexagonal, or other shapes. Substrate 01 is manufactured from a wafer thinning process with a thickness of less than 300 μm, which facilitates thinning of the packaged device.

[0043] The diaphragm is a rigid-flexible composite structure, consisting of an oxide layer 05, an organic flexible film, and an insulating layer 07, mounted on a substrate 01. Its two sides are fixed to the substrate 01. The rigid oxide layer 05 can be made of silicon dioxide, silicon nitride, aluminum oxide, or silicon carbide, which have low density and high Young's modulus. The dry film 08 is applied through a lamination process, covering the slots in the rigid material. Its width is greater than the slot width. The selection of the dry film 08 must meet the following criteria: 1) Compatible with MEMS technology, capable of performing processes such as bonding, exposure, and etching; 2) Reliability issues: dustproof, waterproof, and insulating, while ensuring that rigid material panels fit together and that film tearing, delamination, or peeling does not occur under varying humidity conditions, stress, or excitation; 3) Flexible materials can withstand high temperatures and withstand the temperature of the SMD packaging process without causing reliability issues in the device, such as cracking of rigid materials; 4) The flexible material must have a certain stretchability to prevent damage when the device is deflected. The flexible material can be selected from, but is not limited to, the following: PI, Flexfiner SA, PDMS, Parylene C, PVI-3, or other organic films. Its thickness should be between 0.5 μm and 30 μm, preferably between 0.5 μm and 25 μm.

[0044] Dry film 08 uses a flowable, curable polymer flexible material to cover and fill the slotted gaps and slotted areas, forming a covering flexible film after curing. When the piezoelectric composite unit 09 is driven by an electrical signal to cause the diaphragm to displace and emit sound, it can prevent sound leakage and prevent gas from escaping from the slotted gaps, thereby improving the output sound pressure level of the MEMS sound chip in the low-frequency band. At the same time, when the diaphragm is divided into multiple unconnected cantilever structures, the dry film 08 can be used to connect the various parts to form a vibrating whole. After processing, the posture of each part remains consistent and moves up and down together as a whole when driven. The slotted part is covered and filled with flexible material, which reduces the moving mass of the diaphragm, making it easier to produce larger vibration amplitudes, thereby achieving greater excursion. When the force of the electrodes is equal, the lower the mass, the greater the diaphragm acceleration, and the higher the sound pressure level (SPL) achieved at high frequencies.

[0045] In this embodiment, a polymer layer, such as polyimide or silicone rubber, is spin-coated on the diaphragm surface. This material's viscoelastic properties dissipate vibration energy, effectively increasing mechanical damping. This directly reduces unnecessary excitation from subharmonics, preventing resonance-induced diaphragm excursion and the resulting significant nonlinearity. The PI damping layer (2µm thick) reduces the diaphragm's mechanical quality factor (Q) from 6.3 to 3.1, and improves peak SPL fluctuation from ±8dB to ±3dB.

[0046] The actuator unit includes one or more piezoelectric composite units 09. Each piezoelectric composite unit 09 includes: The piezoelectric composite unit comprises at least two electrode layers and at least one piezoelectric layer. A piezoelectric layer is provided between two adjacent electrode layers to structurally decouple the MEMS sound chip and simultaneously release the process internal stress of each membrane layer, thereby achieving a larger drive displacement and sound pressure level output. The piezoelectric composite unit 09 is made of at least one material selected from single crystal AlN, doped AlN, PZT, and ZnO, with a thickness of 0.25 to 10 μm. For example, the piezoelectric composite unit 09 includes a bottom electrode layer, a piezoelectric layer, and a top electrode layer.

[0047] In combination with the first aspect, an insulating layer 07 is further provided on a side of the piezoelectric composite unit 09 close to the substrate 23 .

[0048] The insulating layer 07 of the top electrode layer of the piezoelectric composite unit 09 primarily isolates the patterned piezoelectric composite unit 09, preventing electrical connection between the upper and lower electrodes while also providing electrical insulation and isolation protection. A passivation layer is deposited on the patterned piezoelectric composite unit 09 for insulation protection, isolating the electrical connection between the top and bottom electrode layers and providing insulation and protection. The patterned passivation layer also provides access to the bottom and top electrode layers, electrical connections between different piezoelectric composite units 09, and substrate electrical pads 16 on connection pads 17. The passivation layer must have excellent step coverage and be able to adhere tightly to each film layer. The material can be selected from, but is not limited to, one or a combination of the following: silicon dioxide, aluminum nitride, PI, aluminum oxide, and other oxide insulating materials, with a thickness of 0.05 μm to 1 μm.

[0049] In this embodiment, periodic through-holes 02 are machined into the diaphragm or support structure within the MEMS sound chip. This array of through-holes 02 alters the acoustic wave propagation path, reducing reflective coupling. Viscous losses are generated when acoustic waves pass through the through-holes 02, thereby suppressing resonance. The packaging cap 11 is made of metal or ceramic, and its openings 12 are arranged in a circular, square, or polygonal array, positioned close to the diaphragm's effective vibration area.

[0050] It's understandable that resonant cavities can be used to enhance specific frequencies of sound. MEMS devices can also potentially improve sound pressure levels by designing appropriate resonant cavities. By properly adjusting the shape and size of through-hole 02 and chip cavity 04, or by incorporating acoustic impedance matching structures, sound waves can be better radiated.

[0051] In combination with the first aspect, a limiting unit 03 is provided in the MEMS sound chip to limit the displacement amplitude of the diaphragm at the resonant frequency, thereby further reducing the nonlinearity and total harmonic distortion of the MEMS sound device caused by the resonant frequency.

[0052] In combination with the first aspect, the packaging cap 11 can be made of aluminum alloy, stainless steel, nickel-plated copper or ceramic, and its openings 12 are arranged in a circular, square or polygonal array, and the openings 12 are located close to the effective vibration area of ​​the diaphragm.

[0053] The packaging cap 11 needs to select a packaging material with good acoustic impedance matching, high rigidity and moderate density, such as a metal alloy, which can better transmit vibration, increase the sound pressure level, optimize acoustic matching, and reduce the energy absorption of the MEMS sound chip vibration. The packaging cap 11 uses a metal shell with an array-type opening 12, which is conducive to enhancing the radiation of specific frequency sound and improving the sound pressure level.

[0054] In combination with the first aspect, there are multiple openings, and the multiple openings are arranged in an array.

[0055] It can be understood that, depending on the size of the package, a large single opening 12 can be opened outside the package, or multiple small openings 12 of various shapes (circular, square, oval, hexagonal, etc., with circular shapes being preferred) can be opened. The multiple small openings 12 are arranged in a regular array, and the openings 12 should be as close as possible to the effective vibration area of ​​the diaphragm.

[0056] In conjunction with the first aspect, an adhesive layer 14 is provided between the package cap 11 and the substrate 23, sealingly connecting the package cap 11 to the substrate 23. This adhesive layer 14 is solder paste. The joint 15 between the MEMS sound chip and the substrate 23 is filled with epoxy resin for a sealed connection.

[0057] In the second aspect, the embodiment of the present application also provides a method for preparing a MEMS micro speaker packaging structure, combining Figure 8 As shown, the method includes: S110, providing MEMS wafers and substrates.

[0058] S120, back grinding, laser grooving and dicing of the MEMS wafer into independent MEMS sound chips.

[0059] S130, flip-chip soldering the MEMS sound chip to the substrate, and filling non-conductive glue at the bottom of the MEMS sound chip to fix and seal the soldering points.

[0060] S140, setting solder paste on the surface of the substrate, installing a packaging cap with an acoustic opening to wrap the MEMS sound chip.

[0061] First, the back of the wafer is masked to reduce its thickness. Laser grooving and dicing are then performed to separate the wafer into individual MEMS sound chips. A cavity structure is provided on the substrate in the thickness direction corresponding to the vibration area of ​​the MEMS sound chip diaphragm. This cavity is larger than the size of the MEMS sound chip diaphragm to prevent the edge of the diaphragm from colliding with the cavity sidewalls during vibration, thus avoiding noise and mechanical damage. This also eliminates standing waves formed by sound waves reflected within the narrow cavity, reducing high-frequency distortion. The depth of the cavity is significantly greater than the maximum excursion of the diaphragm in the thickness direction, ensuring that the diaphragm does not bottom out at maximum amplitude (avoiding collision with the cavity bottom), ensuring linear vibration. A MEMS sound chip diaphragm stopper 18 is provided on the substrate 23 to limit the resonant frequency amplitude, and multiple vent holes 21 are provided on the back. By optimizing the substrate cavity size, as well as the size, location, and number of the vent holes, the acoustic performance of the MEMS speaker can be optimized, improving the smoothness of the high-frequency band of the frequency response curve.

[0062] A MEMS dustproof and sound-transmitting membrane is attached to the substrate 23 to prevent dust and water, thereby improving the reliability of the device.

[0063] Subsequently, flip-chip welding is performed to implant solder ball bumps at the conductive PAD06 position of the MEMS sound chip. The cut MEMS sound chip is directly flipped over and pasted face down on the target position of the substrate 23. Then, the conductive PAD06 of the MEMS sound chip is aligned and bonded to the electrode contacts of the substrate 23 through solder welding, hot pressing welding or conductive adhesive bonding to electrically connect to the substrate 23.

[0064] Subsequently, the pasted MEMS sound chip is fixed by filling glue (non-conductive material) on the substrate 23 and filling the gap at the bottom of the sealed chip to protect the welding bumps and ensure the structural stability of the MEMS chip package.

[0065] Finally, solder paste is placed on the substrate 23 and the packaging cap 11 is fixed to wrap the MEMS sound chip.

[0066] In conjunction with the second aspect, before step S110, the MEMS sound chip is prepared, which specifically includes: S010, performing RIE etching on the pre-treated substrate to obtain a groove of a specified size.

[0067] After the substrate (i.e., chip substrate 01) has completed surface pretreatment (such as cleaning and drying), the surface of the chip substrate 01 is precisely etched using a reactive ion etching (RIE) process to form a groove with a specific structure, thereby forming a chip cavity 04, such as Figure 10In this embodiment, the length and width of the groove need to be controlled within the range of 10um to 5000um, and the depth is controlled between 0.5um and 10um to meet the precise requirements of the subsequent device structure on morphology and size.

[0068] In this step, the RIE process achieves high-precision anisotropic etching, ensuring steep groove sidewalls and a flat bottom, providing a reliable foundation for constructing the device's functional areas. Furthermore, the substrate 01 material is not limited to silicon; alternative materials such as glass and sapphire can also be used. Therefore, RIE process parameters must be adjusted according to the specific material properties to achieve the ideal etching effect.

[0069] S020, filling the groove with a sacrificial layer, and making the substrate surface flat and smooth by grinding and polishing.

[0070] Combine Figure 11 As shown, the sacrificial layer material may be PSG, silicon oxide, polysilicon, PI or other suitable materials.

[0071] S030 , growing barrier layers on the front and back surfaces of the substrate, and generating a support layer and a functional layer on the front surface.

[0072] First, a double-sided thermal oxidation barrier layer (silicon dioxide layer) is grown. Usually, in a high-temperature (e.g., 1000-1200°C) oxygen environment, a silicon dioxide (SiO2) film is generated on the surface of the silicon substrate through a thermal oxidation reaction. The thickness of the barrier layer is usually 0.1um-5um, and the preferred thickness is 1um.

[0073] The barrier layer grown on the front side is used to prevent chemical reactions or impurity diffusion between the subsequently grown piezoelectric layer, electrode layer and the substrate; a barrier layer is also formed on the back side to prevent contamination or stress damage to the back side of the wafer during subsequent processing.

[0074] Subsequently, a support layer is grown on the front side to enhance the mechanical strength of the front side structure and reduce the bending or warping of the wafer caused by subsequent processes (such as thin film deposition and etching). Subsequently, a seed layer, a piezoelectric layer and an electrode layer are deposited.

[0075] The seed layer facilitates high-quality growth of the piezoelectric layer. The piezoelectric layer is a single-crystal PZT film with a thickness of 2 μm, and the top electrode is a Pt film with a thickness of 0.1 μm. The piezoelectric layer can be made of, but is not limited to, one or a combination of the following materials: polycrystalline or single-crystal piezoelectric films such as ZnO, AlN, PZT, and PVDF, or doped piezoelectric films such as AlN. The thickness of the piezoelectric layer ranges from 0.1 μm to 15 μm. Excessive lattice mismatch can lead to cracks or amorphization in the PZT layer. This can be optimized by adjusting the seed layer material (for example, to make the lattice constant of ZrO2 closer to that of PZT).

[0076] Subsequently, a top electrode layer is deposited. The electrode material may be selected from, but is not limited to, one or a combination of the following: single-crystalline or polycrystalline metal films such as aluminum, copper, gold, platinum, molybdenum, chromium, and titanium; conductive metal films such as lanthanum nickel oxide (LNO) and SRO; or composite metal layers such as a gold / chromium composite layer. Preferably, the thickness of the Pt electrode is between 0.01 μm and 5 μm.

[0077] S040, patterning and etching the piezoelectric layer and the electrode layer.

[0078] The PZT piezoelectric film is etched at an angle to facilitate step coverage of the passivation layer. The PZT piezoelectric film etch angle is 30°-60°, and the bottom electrode overetching is less than 10%. (Whether this should be specified in the claims is acceptable.) The PZT sidewall roughness is minimized. The goal is to achieve zero delamination between the sliced ​​PZT and the passivation layer after passivation layer deposition. The silicon dioxide layer prevents the etchant from attacking the substrate, and the seed layer ensures the positioning accuracy of the etch stop layer.

[0079] S050, depositing a passivation layer and patterning it, and forming metal traces and pads through a lift-off process.

[0080] A deposited passivation layer isolates the electrical connections between the electrode layers, providing insulation and protection to prevent short circuits. A patterned passivation layer leads to the bottom and top electrode layers, providing electrical connections between the different piezoelectric composite units and connecting the electrical pads 16 on the substrate to the pads 17. The passivation layer is made of silicon dioxide with a thickness of 0.5 μm. The lift-off metal pads and traces can be made of, but are not limited to, one or a combination of the following materials: gold, copper, aluminum, other metals, or conductive alloys.

[0081] The passivation layer needs to have good step coverage and be able to fit tightly onto each film layer. The material can be selected from, but not limited to, one or a combination of the following: TEOS, silicon dioxide, aluminum nitride, PI, aluminum oxide, and other oxide insulating materials, or non-conductive organic compounds.

[0082] S060, vacuum lamination of flexible dry film, photolithography patterning.

[0083] A flexible protective layer is formed on the device surface to reduce wafer bending (CTE matching) and prevent mechanical damage. This dry film 08 covers metal connections (such as the PADs and traces in step S05) to isolate moisture, oxygen, and ion contamination from the environment. Photolithography is used to define key areas such as cavity release holes and pads (PADs), ensuring precise alignment for subsequent processes.

[0084] The dry film 08 not only needs to be compatible with MEMS processes, be able to be patterned, work for a long time, be resistant to aging, and have good mechanical properties and temperature stability, but also requires a certain elongation rate and the (CTE) difference between the material and the substrate to minimize the wafer bending. It uses PI, alumina, silicon carbide, and other dry film materials such as Flexfiner SA and PVI-3, as well as organic films such as polyimide, polyparaxylene, and polyurethane, with a thickness ranging from 0.5um to 30um.

[0085] S070 , thinning the substrate and forming a cavity on the back side of the substrate by DRIE etching.

[0086] Chemical mechanical polishing (CMP) thins the substrate to 300 μm, reducing device mass and improving the response sensitivity and mechanical flexibility of the MEMS device. Using DRIE (deep reactive ion etching) to etch a cavity on the back of the substrate provides space for MEMS devices (such as resonant structures) and optimizes the device's vibration freedom.

[0087] Through substrate thinning and back-side DRIE etching, the lightweighting of MEMS devices and the precise release of cavity structures are achieved.

[0088] S080, removing the sacrificial layer and the oxide layer to form a cavity structure, thereby obtaining a MEMS sound chip.

[0089] The sacrificial layer can be made of polystyrene (PSG), silicon oxide, polysilicon, PI, or other suitable materials. When using PSG, wet etching is performed using a mixture of HNO3 and HF to etch the PSG within the silicon wafer cavity. Wet etching removes the oxide layer 05. By selectively removing the sacrificial layer, the movable portion of the MEMS device (such as a resonator or micromirror) is separated from the substrate or support layer, enabling free vibration or movement. This ensures that the cavity surface is free of residue, thus preventing negative impacts on device performance (such as sensitivity and resonant frequency).

[0090] Combine Figure 4 、 Figure 5 As shown, the opening 12 of the packaging cap 11 can also be opened on the side, combined with Figure 6 As shown, the packaging cap 11 can also be directly connected to the MEMS sound chip through the adhesive layer 14. Figure 7 As shown, the packaging cap 11 may have multiple openings 12, which can be selected and used according to actual usage requirements. This is only an example and not a limitation.

[0091] The MEMS sound chip of the same specification is packaged in different forms, where D00 is a conventional gold wire PCB substrate package, and D01 is packaged according to the packaging form of the present invention. Acoustic tests are performed on these packaged samples, and the frequency F and sound pressure level SPL curves of the sample devices are obtained as shown above. Figure 9 The two blue curves in the upper middle and the frequency F-total harmonic distortion THD curve are as follows Figure 9 The orange and green curves in the lower middle.

[0092] from Figure 9 A comparison shows that the sound pressure level (SPL) between the frequencies of 6kHz and 16.5kHz has decreased, with the maximum decrease of 15dB, and the sound pressure level (SPL) between the frequencies of 16.5kHz and 20kHz has increased, with the maximum increase of about 15dB; for the frequency-total harmonic distortion (THD) curve, the D01 sample has a significant improvement compared to the D00 in the mid-high frequency range near 4.2kHz, 14kHz, and the frequency range after 18.2kHz, especially in the distortion caused by the second harmonic near 4.2kHz, the THD has been reduced from the original 9% to about 5%, and the THD near 14kHz has also been greatly reduced. The new packaging form makes the THD of the D01 sample less than 5% overall in the entire frequency curve range, which improves the acoustic performance of the device to a certain extent and effectively reduces the total harmonic distortion of the device.

[0093] Those skilled in the art will clearly understand that, for the convenience and brevity of description, the specific working processes of the above-described systems and devices can refer to the corresponding processes in the aforementioned method embodiments and will not be repeated here.

[0094] In addition, in the description of the embodiments of the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral connections; they may refer to mechanical connections or electrical connections; they may refer to direct connections or indirect connections through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0095] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0096] Finally, it should be noted that the above embodiments are only specific implementation methods of the present invention, which are used to illustrate the technical solutions of the present invention, rather than to limit them. The scope of protection of the present invention is not limited thereto. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that any person skilled in the art can modify or easily conceive of changes to the technical solutions described in the above embodiments within the technical scope disclosed by the present invention, or replace some of the technical features therein with equivalents. Such modifications, changes or replacements do not deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A MEMS micro speaker packaging structure, characterized in that: The packaging structure includes: The base plate has a hollow cavity structure, a limiting device, and multiple ventilation holes at the bottom; A MEMS sound chip is mounted upside down on the substrate, with its edge region bonded to the substrate via a connection, and a diaphragm of the MEMS sound chip can vibrate up and down relative to the substrate along a lifting axis; A packaging cap, covering the MEMS sound chip, with an opening on its upper surface, and two bottom sides connected to the substrate, surrounding the outer edge of the MEMS sound chip substrate; The dual-acoustic cavity structure includes an upper acoustic cavity and a lower acoustic cavity. The upper acoustic cavity is formed by the cavity of the MEMS sound chip, the through hole and the packaging cap; the lower acoustic cavity is surrounded by the MEMS sound chip and the substrate, and is connected to the external environment through the vent hole. Microporous film elements cover the vent holes of the substrate to achieve dust and water resistance and air pressure balance; Among them, the MEMS sound chip is provided with a cavity and multiple through holes inside. The size of the through holes is much smaller than the size of the cavity. The sound waves propagate upward through the cavity and the through holes, and then propagate through the opening of the packaging cover to the external environment.

2. The packaging structure according to claim 1, wherein: The MEMS sound chip at least includes a substrate, a piezoelectric composite unit, a diaphragm and an electrode PAD; the material of the piezoelectric composite unit is selected from at least one of single crystal AlN, doped AlN, PZT and ZnO, and the thickness is 0.25~10um.

3. The packaging structure according to claim 1, wherein: The MEMS sound chip is provided with a limiting unit for limiting the displacement amplitude of the diaphragm at the resonant frequency.

4. The packaging structure according to claim 2, wherein: The packaging cap is made of metal or ceramic, and its openings are arranged in a circular, square or polygonal array, and the openings are located close to the effective vibration area of ​​the diaphragm.

5. The packaging structure according to claim 1, wherein: The opening is single or multiple, and the multiple openings are arranged in an array.

6. The packaging structure according to claim 2, wherein: An insulating layer is further provided on a side of the piezoelectric composite unit close to the substrate.

7. The packaging structure according to claim 1, wherein: An adhesive layer is provided between the packaging cap and the substrate, and the material is solder paste.

8. A method for preparing a MEMS micro-speaker packaging structure, characterized in that: include: Provide MEMS wafers and substrates; Back grinding, laser grooving and scribing the MEMS wafer into independent MEMS sound chips; Flip-chip soldering the MEMS sound chip to the substrate, and filling non-conductive glue at the bottom of the MEMS sound chip to fix and seal the soldering points; Solder paste is provided on the surface of the substrate, and a packaging cap with an acoustic opening is installed to wrap the MEMS sound chip.

9. The method according to claim 8, characterized in that Before providing the MEMS wafer and substrate, the following steps are also included: Performing RIE etching on the pre-treated substrate to obtain a groove of a specified size; Filling the groove with a sacrificial layer, and making the surface of the substrate flat and smooth by grinding and polishing; growing barrier layers on the front and back sides of the substrate, and forming support layers and functional layers on the front side; Patterning and etching the piezoelectric layer and the electrode layer; Deposit and pattern the passivation layer, and form metal traces and pads through a lift-off process; Vacuum lamination of flexible dry film and photolithography patterning; Thinning the substrate and forming a cavity on the back side of the substrate by DRIE etching; The sacrificial layer and the oxide layer are removed to form a cavity structure, thereby obtaining a MEMS wafer.

10. The method according to claim 9, characterized in that The size of the cavity of the substrate is larger than the size of the diaphragm in the MEMS sound chip, and the depth of the cavity is larger than the maximum offset of the diaphragm.

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