A packaging structure to reduce THD of MEMS piezoacoustic devices

Abstract

This utility model relates to the field of chip packaging technology, and more particularly to a packaging structure for reducing the total harmonic distortion (THD) of MEMS piezoacoustic devices. The structure includes: a substrate having a hollowed-out cavity, a limiting device, and multiple vent holes at the bottom; and a MEMS sound-emitting chip, inverted and soldered onto the substrate, with its edge region bonded to the substrate via a connection point to form a first acoustic cavity. This utility model provides a packaging structure for reducing the THD of MEMS piezoacoustic devices. The inverted soldering of the MEMS sound-emitting chip effectively reduces the volume while ensuring packaging stability. The diaphragm of the MEMS sound-emitting chip and the substrate form the first acoustic cavity, while the chip, substrate, and shell together form a second acoustic cavity. Through dual-cavity air pressure balance, mechanical limiting, and acoustic path optimization, nonlinear vibration is reduced, significantly lowering the total harmonic distortion (THD) of the MEMS piezoacoustic device and improving sound radiation efficiency.

Description

Technical Field

[0001] This application relates to the field of chip packaging technology, and in particular to a packaging structure for reducing the THD of MEMS piezoacoustic devices. Background Technology

[0002] Traditional dynamic loudspeakers are large, require manual or semi-automatic operation, and are expensive. MEMS (Micro-Electro-Mechanical Systems) fabrication technology based on thin-film materials can effectively reduce the size of MEMS sound-generating chips and enable mass production to lower costs. Because MEMS sound-generating chips are small, thin, and their structure cannot be directly exposed to the external environment, a packaging structure is needed to protect them, enabling fully automated assembly and forming a multifunctional MEMS micro-acoustic system. The packaged device has a small size and thin profile, can withstand SMT 260℃ reflow soldering, and can be soldered onto a PCB, thus reducing the complexity and cost of system integration. In in-ear headphone applications, it requires minimal space and weight.

[0003] In traditional MEMS speaker chip packaging technologies, MEMS loudspeakers are packaged with MEMS speakers, metal casings, and substrates. Electrical connections between the substrate and the MEMS speaker chip (PAD) are achieved via metal leads. This approach typically increases package size, has lower reliability, and makes it difficult to improve the acoustic performance of the packaged MEMS loudspeaker. Furthermore, MEMS speakers made of silicon and piezoelectric thin films have a relatively high quality factor (Q factor), typically 100±40. When the voltage-driven signal frequency matches the MEMS speaker chip's resonant frequency, the diaphragm resonance experiences a significant shift, leading to considerable nonlinearity. This results in a narrow, high-peaking peak in the displacement-frequency response curve, causing total harmonic distortion and degraded sound quality in the MEMS loudspeaker. Utility Model Content

[0004] In view of this, the purpose of this utility model is to provide a packaging structure that reduces the THD of MEMS piezoacoustic devices.

[0005] In a first aspect, embodiments of the present invention provide a packaging structure for reducing the THD of MEMS piezoacoustic devices, comprising:

[0006] The substrate has a hollow cavity formed by hollowing out, a limiting device, and multiple ventilation holes at the bottom;

[0007] The MEMS sound-emitting chip is flip-chip bonded to a substrate, and its edge area is bonded to the substrate through a connection to form a first sound cavity. The first sound cavity is connected to the external environment through a vent hole. The diaphragm of the MEMS sound-emitting chip can vibrate up and down relative to the substrate along the lifting axis. Limiting units are provided on the inner side of the chip substrate of the MEMS sound-emitting chip.

[0008] The encapsulation shell covers the MEMS sound-emitting chip, and has acoustic openings on its upper or side surfaces. The bottom sides are connected to the substrate, and the outer edge of the chip substrate surrounding the MEMS sound-emitting chip forms a second acoustic cavity.

[0009] The MEMS sound chip has a cavity and multiple through holes inside. The size of the through holes is smaller than that of the cavity. Sound waves propagate to the second sound cavity through the cavity and through holes.

[0010] In conjunction with the first aspect, the packaging structure also includes:

[0011] Acoustic mesh is used to cover the ventilation holes, achieving dust and water protection and air pressure balance.

[0012] In conjunction with the first aspect, the acoustic mesh is made of expanded polytetrafluoroethylene.

[0013] In conjunction with the first aspect, the depth of the hollow cavity in the substrate is greater than the maximum amplitude of the diaphragm in the MEMS sound-emitting chip.

[0014] In conjunction with the first aspect, the MEMS sound-generating chip also includes a chip substrate, a piezoelectric composite unit, and an electrode PAD; a diaphragm is disposed on the substrate and the edge of the diaphragm is connected to the chip substrate, and at least one piezoelectric composite unit is disposed on the diaphragm.

[0015] In conjunction with the first aspect, the diaphragm material is photosensitive polyimide PI, PVI-3, polyethylene terephthalate PET, polydimethylsiloxane PDMS, or parylene C, with a thickness of 0.5~25um.

[0016] In conjunction with the first aspect, the piezoelectric composite unit includes at least two electrode layers and at least one piezoelectric layer, with a piezoelectric layer disposed between two adjacent electrode layers; the electrode layer material is one of Mo, Au, Pt, Al, Cu or their alloys, and the thickness is 0.01~1.5 μm.

[0017] In conjunction with the first aspect, the encapsulation shell is made of metal alloy or ceramic material, the acoustic opening is circular, square or polygonal, and the position of the acoustic opening is close to the effective vibration area of ​​the diaphragm.

[0018] In conjunction with the first aspect, there are multiple acoustic openings, arranged in an array.

[0019] In conjunction with the first aspect, the substrate and the MEMS sound-emitting chip are electrically connected by solder balls or conductive adhesive, and the connection is sealed with non-conductive adhesive.

[0020] The present invention provides the following beneficial effects: This application provides a packaging structure for reducing the THD of MEMS piezoacoustic devices, comprising: a substrate having a hollow cavity formed by hollowing out, a limiting device, and multiple vent holes at the bottom; a MEMS sound-emitting chip flip-chip bonded to the substrate, the edge region of which is bonded to the substrate through a connection to form a first acoustic cavity, the first acoustic cavity being connected to the external environment through vent holes and capable of vibrating up and down relative to the substrate along a lifting axis; a limiting unit is provided in the chip substrate of the MEMS sound-emitting chip; a packaging shell covering the MEMS sound-emitting chip, having acoustic openings on its upper or side surfaces, and its bottom sides being connected to the substrate, forming a second acoustic cavity around the outer edge of the chip substrate of the MEMS sound-emitting chip; wherein, the MEMS sound-emitting chip has a cavity and multiple through holes inside, the size of the through holes being smaller than the size of the cavity, and sound waves propagate to the second acoustic cavity through the cavity and through holes.

[0021] This invention provides a packaging structure that reduces the total harmonic distortion (THD) of MEMS piezoacoustic devices. The MEMS sound-emitting chip is inverted and sealed, which effectively reduces the size while ensuring the stability of the packaging. The MEMS sound-emitting chip and the substrate form a first acoustic cavity, and together with the substrate and the packaging shell, they form a second acoustic cavity. Through dual-cavity air pressure balance, mechanical limiting, and acoustic path optimization, the total harmonic distortion of MEMS piezoacoustic devices is significantly reduced, and the acoustic radiation efficiency of the devices is improved. At the same time, the edge limiting unit and limiting device physically constrain the diaphragm offset at the resonant frequency, reducing nonlinear vibration.

[0022] Other features and advantages of this invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objectives and other advantages of this invention are realized and obtained through the structures particularly pointed out in the description, claims, and drawings.

[0023] To make the above-mentioned objectives, features and advantages of this utility model more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0024] To more clearly illustrate the specific embodiments of this application or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0025] Figure 1 A schematic diagram of a packaging structure for reducing THD of MEMS piezoacoustic devices provided in an embodiment of this utility model;

[0026] Figure 2 A front view of the MEMS sound-emitting chip D01 provided in this embodiment of the present utility model;

[0027] Figure 3 for Figure 2 A cross-sectional schematic diagram of the provided MEMS sound-emitting chip D01;

[0028] Figure 4 A schematic diagram of the packaging structure for reducing THD of MEMS piezo-acoustic devices provided in this embodiment of the present invention, with the acoustic opening located on the right side;

[0029] Figure 5 A schematic diagram of the packaging structure for reducing THD of MEMS piezo-acoustic devices provided in this embodiment of the present invention, with the acoustic opening located on the left side;

[0030] Figure 6 A schematic diagram of the structure of the package for reducing THD of MEMS piezoacoustic devices provided in this embodiment of the present invention, when the package is connected to the MEMS sound-generating chip DO1 through an adhesive layer;

[0031] Figure 7 A schematic diagram of the packaging structure for reducing THD of MEMS piezo-acoustic devices provided in this embodiment of the present invention, showing that the acoustic openings are multiple and spaced apart.

[0032] Figure 8 The figure shows the test results of the acoustic performance of MEMS piezoelectric acoustic devices with different packaging forms.

[0033] The attached figures are labeled as follows:

[0034] 01-Chip substrate, 02-Through hole, 03-Limiting unit, 04-Cavity, 05-Oxide layer, 06-Electrode PAD, 07-Insulating layer, 08-Dry film, 09-Piezoelectric composite unit;

[0035] 11 - Encapsulation shell, 12 - Acoustic opening, 13 - Second acoustic cavity, 14 - Adhesive layer, 15 - Connection, 16 - Substrate electrical PAD, 17 - Solder pad, 18 - Limiting device, 19 - First acoustic cavity;

[0036] 21-Ventilation hole, 22-Acoustic mesh, 23-Substrate. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0038] To facilitate understanding of this embodiment, the application scenarios and design concepts of this application embodiment will be briefly introduced below.

[0039] Traditional MEMS loudspeakers have large packaging size, low reliability, and excessive total harmonic distortion (THD), which seriously affects sound quality.

[0040] Based on this, this application provides a packaging structure for reducing the THD of MEMS piezoacoustic devices.

[0041] Example 1

[0042] This application provides a packaging structure for reducing the THD of MEMS piezoacoustic devices, combined with Figure 1 As shown, the structure includes: a substrate 23, a MEMS sound-emitting chip, and a packaging shell 11.

[0043] The substrate 23 has a hollow cavity formed by hollowing out, a limiting device 18, and multiple ventilation holes 21 at the bottom.

[0044] The MEMS sound-emitting chip is flip-chip bonded to the substrate 23, and its edge area is bonded to the substrate 23 through the connector 15 to form a first sound cavity 19. The first sound cavity 19 is connected to the external environment through the vent 21. The diaphragm of the MEMS sound-emitting chip can vibrate up and down relative to the substrate 23 along the lifting axis. Limiting units 03 are provided on the inner side of the chip substrate 01 of the MEMS sound-emitting chip.

[0045] The encapsulation shell 11 covers the MEMS sound-emitting chip, and its upper or side surface is provided with acoustic openings 12. The bottom sides are connected to the substrate 23, and the outer edge of the chip substrate 01 surrounding the MEMS sound-emitting chip forms a second acoustic cavity 13.

[0046] The MEMS sound chip has a cavity 04 and multiple through holes 02 inside. The size of the through holes 02 is much smaller than that of the cavity 04. The sound waves propagate to the second sound cavity 13 through the cavity 04 and the through holes 02.

[0047] This invention provides a packaging structure for reducing the total harmonic distortion (THD) of MEMS piezoacoustic devices. The flip-chip bonding of the MEMS sound-generating chip effectively reduces the size while ensuring packaging stability. The combination of the internal cavity 04 and through-hole 02 of the inverted MEMS sound-generating chip actively filters high-frequency harmonics. Through dual-cavity air pressure balance, mechanical limiting, and acoustic path optimization, the total harmonic distortion of the MEMS piezoacoustic device is significantly reduced, improving the device's acoustic radiation efficiency. Simultaneously, the edge limiting unit 03 and limiting device 18 physically constrain the diaphragm offset at the resonant frequency, reducing nonlinear vibration.

[0048] In conjunction with the first aspect, the packaging structure also includes: an acoustic mesh 22, which covers the vent holes 21 of the substrate 23 to achieve dust and water protection and air pressure balance.

[0049] In conjunction with the first aspect, the material of acoustic mesh 22 is expanded polytetrafluoroethylene.

[0050] An acoustic mesh 22 is covered on the ventilation holes 21 of the substrate 23. The acoustic mesh 22 is made of a flexible and elastic microporous material—polytetrafluoroethylene (e-PTFE). The polytetrafluoroethylene microporous material has high porosity and uniform pore size distribution. It is breathable, has a low coefficient of friction and extremely low adsorption. It is not only dustproof, but also oleophobic and hydrophobic, and has thermal stability. It is resistant to chemical corrosion and UV protection. It has a wide operating temperature range of -40~150°C and can continuously perform its breathable function. It is also a waterproof and breathable membrane that is bidirectionally water-blocking and breathable, eliminates fog, maintains internal and external balance, and has waterproof and sound-transmitting effects.

[0051] In conjunction with the first aspect, the depth of the hollow cavity in the substrate 23 is greater than the maximum amplitude of the diaphragm in the MEMS sound-emitting chip.

[0052] 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-generating chip is connected to the external environment through the vent 21, while the other areas are sealed spaces. The depth of the hollow cavity is much greater than the maximum offset of the diaphragm in the MEMS sound-generating unit, thus providing sufficient space for the diaphragm to vibrate vertically. The vent 21 on the substrate 23 is used to reduce the obstruction of air damping on the diaphragm, which is beneficial to improving the sound pressure level. It is understood that a suitable size and distribution of the vent 21 can optimize the airflow path and further improve the sound pressure level. Increasing the diameter of the vent 21 on the substrate 23 from 0.3 mm to 0.5 mm can improve acoustic impedance matching, and increasing the substrate thickness from 0.5 mm to 0.3 mm is beneficial to reducing bending stiffness. The substrate 23 can be made of PCB, BT, etc., with a thickness of 0.1 mm to 0.5 mm. A pad 17 is provided on the substrate 23, and a substrate electrical PAD 16 is provided on the pad 17. The substrate electrical PAD 16 is connected to the electrode PAD 06 of the MEMS sound chip by means of thermoacoustic, thermo-press welding and other methods.

[0053] In addition, the substrate 23 is provided with positioning and mounting position marks for the MEMS sound chip, so that the MEMS sound chip can be accurately bonded to the substrate electrical PAD16 on the substrate 23 by flip-chip bonding. Glue is filled on the substrate 23 to fix and seal the gap between the MEMS sound chip and the substrate 23, thereby protecting the solder bumps and firmly connecting the MEMS sound chip without loosening.

[0054] In conjunction with the first aspect, the MEMS sound-generating chip includes a chip substrate 01, a piezoelectric composite unit 09, a diaphragm, and an electrode PAD 06; the diaphragm is disposed on the chip substrate 01 and the edge of the diaphragm is connected to the chip substrate 01, and at least one piezoelectric composite unit 09 is disposed on the diaphragm.

[0055] The piezoelectric composite unit 09 material is selected from at least one of single-crystal AlN, doped AlN, PZT, and ZnO, and has a thickness of 0.25~10um.

[0056] Combination Figure 2 The diagram shown is a front view of the MEM sound chip D01. Figure 3 The cross-sectional diagram shown represents the MEMS piezoelectric sound-generating chip D01. The dashed lines in regions 10a, 10b, 10c, and 10d represent the edges of the etched dimensions of the cavity on the back side of the piezoelectric MEMS acoustic transducer. These four dashed lines form a square structure, which is also the boundary line of the device's vibrating thin film (i.e., diaphragm). Deep silicon etching removes the middle layer of silicon in the back cavity, forming a hollow cubic cavity structure, which is then released as the diaphragm structure of the MEMS acoustic transducer. 40a represents the piezoelectric composite unit 09 of the MEMS acoustic transducer. 20a, 20b, 20c, and 20d are gaps extending to the edge region of the cavity, with the other end extending beyond the middle region of unit 40a. The gaps divide 40a in the region near the cavity edge, but 40a remains a single unit with identical electrical components on both sides. The D01 device contains spring-slot structures in regions 30a, 30b, 30c, and 30d. These structures are formed by etching near the four boundaries inside region 40a. The spring structures can be S-shaped, semi-elliptical, or branch-shaped, etc. Under the drive of the piezoelectric signal, the diaphragm of the MEMS piezoelectric sound unit D01 vibrates up and down in a piston-like manner. The straight slots 20a, 20b, 20c, and 20d of the MEMS piezoelectric sound unit D01 are mainly used to release residual stress on the device diaphragm, reducing the risk of diaphragm deformation or even breakage due to stress. At the same time, structural decoupling of the device allows for greater drive displacement and sound pressure level output. The audio drive signal applied to region 40a corresponds to the output sound wave signal. The audio drive signal is generally a sinusoidal signal of DC voltage plus AC voltage, such as DC10V + AC10V, or driven by a bipolar signal.

[0057] Combination Figure 3 The diagram shows a cross-sectional view of the MEMS sound-generating chip D01, which includes a chip substrate 01, a diaphragm, and a piezoelectric composite unit 09.

[0058] The interior of the chip substrate 01 is formed by removing silicon using the DRIE process to create a cavity 04. The chip substrate 01 has a symmetrical structure, and its structure can be square, circular, rectangular, hexagonal, or other shapes. The chip substrate 01 is prepared from a wafer with a thickness of less than 300µm after wafer thinning, which is beneficial for the thinning of packaged devices.

[0059] In conjunction with the first aspect, the diaphragm material is photosensitive polyimide PI, PVI-3, polyethylene terephthalate PET, polydimethylsiloxane PDMS, or parylene C, with a thickness of 0.5~25um.

[0060] The diaphragm is a rigid-flexible composite structure, consisting of an oxide layer 05, an organic flexible film, and an insulating layer 07 disposed on the chip substrate 01, with both sides fixed to the chip substrate 01. The rigid material oxide layer 05 can be selected from materials with low density and high Young's modulus, such as silicon dioxide, silicon nitride, alumina, or silicon carbide. The dry film 08 is laminated using a lamination process, covering a groove in the rigid material, with a width greater than the groove width. The selection of the dry film 08 needs to meet the following conditions:

[0061] 1) Compatible with MEMS processes, enabling processes such as patching, exposure, and etching;

[0062] 2) Reliability issues: dustproof, waterproof and insulating, while ensuring the bonding of rigid material plates, and preventing film tearing, delamination, peeling and other phenomena under different humidity conditions and under stress or excitation.

[0063] 3) Flexible materials can withstand high temperatures and the temperatures of surface mount packaging processes without causing reliability issues in the device, such as causing rigid materials to crack;

[0064] 4) It has a certain elongation, and the flexible material will not be damaged when the device is deflected. The flexible material can be selected from, but is not limited to, one of the following materials: PI, Flexfiner SA, PDMS, Parylene C, PVI-3, or other organic thin films, and its thickness should be between 0.5um and 30um, preferably between 0.5um and 25um.

[0065] The dry film 08 uses a flowable and curable flexible polymer material to cover and fill the slotted gaps and areas, forming a flexible covering film after curing. When the piezoelectric composite unit 09 is driven by an electrical signal to move the diaphragm and produce sound, sound leakage is prevented, and gas does not flow out from the slotted gaps, improving the output sound pressure level of the MEMS sound-generating chip in the low-frequency range. Simultaneously, when the diaphragm is divided into multiple unconnected cantilever structures, the dry film 08 can connect the various parts, forming a unified vibration unit. After processing, the posture of each part remains consistent, moving up and down together as a whole under drive. The slotted parts are covered and filled with flexible material, reducing the diaphragm's moving mass and making it easier to generate larger amplitude vibrations, thus achieving greater displacement. When the electrode forces are equal, the lower the mass, the greater the diaphragm acceleration, resulting in a higher sound pressure level (SPL) at high frequencies. The flexible polymer material has a certain loss factor; increasing damping can reduce the mechanical constraint and energy absorption of the diaphragm movement by the packaging structure. Adding damping material to the non-radiative region can suppress stray modes and improve the efficiency of the dominant mode.

[0066] In conjunction with the first aspect, the piezoelectric composite unit 09 includes: at least two electrode layers and at least one piezoelectric layer, with a piezoelectric layer disposed between two adjacent electrode layers. The electrode layer material is one of Mo, Au, Pt, Al, Cu or their alloys, and the thickness is 0.01~1.5 μm.

[0067] The piezoelectric composite unit 09 is used to structurally decouple the MEMS sound-generating chip and release the process stress of each film layer, thereby achieving greater driving displacement and sound pressure level output. 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 0.25~10µm.

[0068] In conjunction with the first aspect, an insulating layer 07 is also provided on the side of the piezoelectric composite unit 09 near the substrate 23.

[0069] 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 connections between the upper and lower electrodes, and providing electrical insulation and protection. A passivation layer is deposited on the patterned piezoelectric composite unit 09 for insulation protection, isolating the electrical connections between the top and bottom electrode layers, providing insulation and protection. The patterned passivation layer leads to the bottom and top electrode layers, facilitating electrical connections between different piezoelectric composite units 09 and connecting electrode PAD06. The passivation layer needs to have good step coverage, allowing it to adhere tightly to each film layer. Materials can be selected from, but are not limited to, one or a combination of the following: silicon dioxide, aluminum nitride, PI, alumina, and other oxide insulating materials, with a thickness of 0.05µm to 1µm.

[0070] In this embodiment, periodic through-holes 02 are fabricated on the diaphragm or support structure inside the MEMS sound-generating chip. The propagation path of the sound wave is changed by the array of through-holes 02, reducing reflection coupling. When the sound wave passes through the through-holes 02, viscous loss is generated, thereby suppressing resonance. The package shell 11 is made of metal or ceramic material, and its acoustic openings 12 are arranged in a circular, square, or polygonal array, and the acoustic openings 12 are located close to the effective vibration area of ​​the diaphragm.

[0071] Understandably, resonant cavities can be used to amplify sound at specific frequencies, and MEMS devices may also be able to improve sound pressure levels by designing suitable resonant cavities. By reasonably adjusting the shape and size of the through-hole 02 and cavity 04, or by adding acoustic impedance matching structures, sound waves can be radiated more effectively.

[0072] In conjunction with the first aspect, the encapsulation shell 11 is made of metal or ceramic, and its acoustic opening 12 is circular, square or polygonal, and the acoustic opening 12 is located close to the effective vibration area of ​​the diaphragm.

[0073] The packaging shell 11 needs to be made of packaging materials with good acoustic impedance matching, high stiffness and moderate density, such as metal alloys, which can better transmit vibration, improve sound pressure level, optimize acoustic matching and reduce energy absorption of MEMS sound-emitting chip vibration. The packaging shell 11 adopts a metal shell with acoustic openings 12, which is conducive to enhancing the radiation of sound at specific frequencies and improving sound pressure level.

[0074] In conjunction with the first aspect, there are multiple acoustic openings 12, and multiple acoustic openings 12 are arranged in an array.

[0075] Understandably, depending on the package size, a large single acoustic opening 12 can be made outside the package, or multiple acoustic openings 12 of various shapes (circular, square, elliptical, hexagonal, etc., with circular being preferred) can be made. The multiple acoustic openings 12 are arranged in a regular array, and the acoustic openings 12 should be as close as possible to the effective vibration area of ​​the diaphragm.

[0076] In conjunction with the first aspect, the substrate 23 and the MEMS sound-emitting chip are electrically connected by solder balls or conductive adhesive, and the connection is sealed with non-conductive adhesive.

[0077] Specifically, the connection 15 between the MEMS sound-emitting chip and the substrate 23 is filled with non-conductive adhesive (epoxy resin) for sealing. An adhesive layer 14 is provided between the package housing 11 and the substrate 23, which seals the package housing 11 and the substrate 23 together.

[0078] In preparing the above-mentioned packaging structure for reducing the THD of MEMS piezoacoustic devices, the first step is to perform a back mask on the provided wafer to reduce its thickness.

[0079] Subsequently, laser grooving and dicing are performed to cut the wafer into individual MEMS sound-generating chips. The hollow cavity formed by the cutout of the substrate 23 corresponds to the vibration area of ​​the diaphragm of the MEMS sound-generating chip in the thickness direction, and the cross-sectional size of the hollow cavity should be larger than the size of the MEMS sound-generating chip diaphragm to prevent the edge of the diaphragm from colliding with the sidewall of the cavity during vibration, avoiding noise and mechanical damage. At the same time, it eliminates standing waves formed by sound wave reflection in the narrow cavity, reducing high-frequency distortion. The depth of the hollow cavity is much greater than the maximum offset of the diaphragm in the thickness direction, ensuring that the diaphragm does not touch the bottom during maximum amplitude vibration (avoiding collision with the bottom of the cavity), thus ensuring linear vibration. A MEMS sound-generating chip diaphragm limiting device 18 is provided on the substrate 23 to limit the amplitude of the resonant frequency, and multiple ventilation holes 21 are opened on the back of the substrate 23 to optimize the acoustic performance of the device and improve the smoothness of the high-frequency band of the frequency response curve.

[0080] An acoustic mesh 22 is attached to the substrate 23 to provide dust and water protection, thereby improving the reliability of the device.

[0081] Subsequently, flip-chip bonding is performed, and solder ball bumps are implanted at the electrode PAD06 position of the MEMS sound-emitting chip. The cut MEMS sound-emitting chip is directly flipped face down and pasted onto the target position on the substrate 23. Then, the electrode PAD06 of the MEMS sound-emitting chip is aligned and bonded to the electrode contacts of the substrate 23 by soldering, thermoforming, or conductive adhesive bonding to achieve electrical connection with the substrate 23.

[0082] Subsequently, the pasted MEMS sound-emitting chip is fixed and filled and sealed on the substrate 23 by filling (epoxy resin) to protect the solder bumps and reduce the impact of external vibration on the MEMS sound-emitting chip, thus ensuring the stability of the MEMS sound-emitting chip packaging structure.

[0083] Finally, solder paste is placed on substrate 23, and the package shell 11 is then fixed to encapsulate the MEMS sound chip.

[0084] Combination Figure 4 , Figure 5 As shown, the acoustic opening 12 of the encapsulation housing 11 can also be formed on the side, combined with Figure 6 As shown, the package housing 11 can also be directly connected to the substrate 23 via an adhesive layer 14. The adhesive layer 14 can be made of solder paste or silicone adhesive, etc. Figure 7 As shown, the acoustic opening 12 of the encapsulation shell 11 can also be multiple, and can be selected and used according to actual usage requirements. This is only an example and is not limited.

[0085] In MEMS sound-emitting chip packaging, the thermal expansion coefficients of the substrate 23 and the package shell 11 are close to those of the silicon material on the chip substrate 01 of the MEMS sound-emitting chip, while also considering heat dissipation performance. Silicon has a thermal expansion coefficient (CTE) of approximately 2.6 ppm / K at room temperature. Commonly used substrate materials are organic substrates (such as RF-4): with a higher CTE (approximately 12-18 ppm / K), requiring a thermal stress buffer plate (such as glass) for matching. The CTE of the buffer plate is between that of silicon and organic substrates (e.g., 2.6-12 ppm / K). Ceramic substrates (such as alumina): with a CTE of approximately 7 ppm / K, although higher than silicon, are closer to the CTE of silicon than organic substrates, and are often used for high-reliability packaging. Metal shells include Cuvar alloy (Fe-Ni-Co): with a CTE of approximately 5-6 ppm / K, close to that of silicon, and are often used for hermetically sealed packaging to reduce thermal stress. Copper or aluminum: Higher CTE (copper 16.5ppm / K, aluminum 23ppm / K), but better thermal conductivity (copper 385W / (m·K)), requiring the use of stress-absorbing structures.

[0086] In this application, the packaging shell 11 is made of nickel-plated aluminum alloy, the substrate is made of ceramic substrate, the MEMS sound chip and the ceramic substrate are connected by silicone adhesive with low stress characteristics CTE (2.6-6.23 ppm / K), and the packaging shell 11 and the substrate 23 are connected by low stress adhesive with CTE typically 10-100 ppm / K.

[0087] Combination Figure 8 As shown, MEMS sound-emitting chips of the same specification were packaged in different ways. D00 was a conventional gold-wire PCB substrate package, while D01 was packaged according to the packaging method of this invention. Acoustic tests were performed on these packaged samples, and the frequency-sound pressure level (SPL) curves of the above sample devices were obtained as shown below. Figure 8 The two blue curves at the top center, and the frequency F-total harmonic distortion (THD) curve, are as follows: Figure 8 The orange and green curves at the bottom center, compared to the graph above, show that the SPL (Sound Pressure Level) decreases between 6kHz and 16.5kHz, with a maximum reduction of 15dB, while the SPL increases between 16.5kHz and 20kHz, with a maximum increase of approximately 15dB. Regarding the THD frequency curve, the D01 sample shows significant improvement over the D0 sample in the mid-to-high frequency ranges around 4.2kHz and 14kHz, and in the frequency range after 18.2kHz. In particular, the THD caused by the second harmonic distortion near 4.2kHz is reduced from 9% to approximately 5%, and there is also a significant reduction in THD near 14kHz. The new packaging design ensures that the overall THD of the D01 sample is less than 5% across the entire frequency range, improving the acoustic performance of the device to a certain extent and effectively reducing the total harmonic distortion.

[0088] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working process of the system and apparatus described above can be referred to the corresponding process in the foregoing method embodiments, and will not be repeated here.

[0089] Furthermore, in the description of the embodiments of this application, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0090] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0091] Finally, it should be noted that the above embodiments are merely specific implementations of this application, used to illustrate the technical solutions of this application, and not to limit them. The protection scope of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that any person skilled in the art can still modify or easily conceive of changes to the technical solutions described in the foregoing embodiments, or make equivalent substitutions for some of the technical features, within the technical scope disclosed in this application. Such modifications, changes, or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be covered within the protection scope of this application. Therefore, the protection scope of this application should be determined by the protection scope of the claims.

Claims

1. A packaging structure for reducing the THD of MEMS piezoacoustic devices, characterized in that, include: The substrate has a hollow cavity formed by hollowing out, a limiting device, and multiple ventilation holes at the bottom; A MEMS sound-emitting chip is flip-chip bonded to the substrate, and its edge region is bonded to the substrate through a connection to form a first acoustic cavity. The first acoustic cavity is connected to the external environment through the vent hole. The diaphragm of the MEMS sound-emitting chip can vibrate up and down relative to the substrate along the lifting axis. A limit unit is provided on the inner side of the chip substrate of the MEMS sound-emitting chip. An encapsulation shell covers the MEMS sound-emitting chip, with acoustic openings on its upper or side surfaces, and its bottom sides connected to the substrate. The outer edge of the chip substrate surrounding the MEMS sound-emitting chip forms a second acoustic cavity. The MEMS sound-emitting chip has a cavity and multiple through holes inside. The size of the through holes is smaller than the size of the cavity. Sound waves propagate to the second sound cavity through the cavity and the through holes.

2. The packaging structure according to claim 1, characterized in that, The packaging structure further includes: An acoustic mesh is used to cover the vents, providing dust and water protection as well as air pressure balance.

3. The packaging structure according to claim 2, characterized in that, The acoustic mesh is made of expanded polytetrafluoroethylene.

4. The packaging structure according to claim 1, characterized in that, The depth of the hollow cavity in the substrate is greater than the maximum amplitude of the diaphragm in the MEMS sound chip.

5. The packaging structure according to claim 4, characterized in that, The MEMS sound-generating chip also includes a chip substrate, a piezoelectric composite unit, and an electrode PAD; the diaphragm is disposed on the substrate and the edge of the diaphragm is connected to the chip substrate, and at least one of the piezoelectric composite units is disposed on the diaphragm.

6. The packaging structure according to claim 4, characterized in that, The diaphragm material is photosensitive polyimide (PI), PVI-3, polyethylene terephthalate (PET), polydimethylsiloxane (PDMS), or parylene (Parylene C), with a thickness of 0.5~25 μm.

7. The packaging structure according to claim 5, characterized in that, The piezoelectric composite unit includes at least two electrode layers and at least one piezoelectric layer, with a piezoelectric layer disposed between two adjacent electrode layers; the electrode layer is made of one of Mo, Au, Pt, Al, Cu or their alloys, and has a thickness of 0.01~1.5 μm.

8. The packaging structure according to claim 1, characterized in that, The encapsulation shell is made of metal alloy or ceramic material, and the acoustic opening is circular, square or polygonal, and the acoustic opening is located close to the effective vibration area of ​​the diaphragm.

9. The packaging structure according to claim 8, characterized in that, There are multiple acoustic openings, and the multiple acoustic openings are arranged in an array.

10. The packaging structure according to claim 1, characterized in that, The substrate and the MEMS sound-emitting chip are electrically connected by solder balls or conductive adhesive, and the connection is sealed with non-conductive adhesive.

Images