MEMS piezoelectric sounder and loudspeaker

Abstract

The utility model provides an MEMS piezoelectric sounder and a loudspeaker, first piezoelectric composite layers are symmetrically arranged at specified edge positions, a plurality of slotted structures are arranged in a specified area, a first diaphragm edge of a formed diaphragm structure is an anchoring edge, and an edge slotted structure is arranged at a non-anchoring edge. The internal stress of each diaphragm layer in the diaphragm structure caused by the process can be reduced by arranging the slotting structure, the flexibility of the diaphragm structure can be improved by covering the slotting structure with the flexible material, meanwhile, the sound leakage of the MEMS piezoelectric sounder at low frequency is reduced, the vibration amplitude and the emission sound pressure level of the MEMS piezoelectric sounder are improved, and the sound quality of the MEMS piezoelectric sounder is improved. According to the MEMS piezoelectric sounder, the flexible material with low density is adopted to replace a silicon vibrating diaphragm with large density, the mass of the vibrating diaphragm structure is reduced, the vibrating diaphragm structure of the rectangular bridge type structure can push out more air, the flexible material increases system damping, a sound pressure level SPL frequency response curve and a THD frequency response curve can be improved, and therefore the tone quality of the MEMS piezoelectric sounder is improved.

Description

Technical Field

[0001] The utility model relates to the technical field of sound generators, in particular to a MEMS piezoelectric sound generator and a loudspeaker. Background Art

[0002] In order to make MEMS (Micro-Electro-Mechanical System) sound-generating devices and speakers more widely used, the industry is committed to designing high-yield, small-sized, high-sound-pressure-level MEMS piezoelectric sounders. However, devices based on silicon substrates and piezoelectric film materials often find it difficult to balance small size and high-sound-pressure-level output. In addition, the damping of the MEMS piezoelectric sounder is small, the quality factor of the device resonance is large, and the displacement at the resonant frequency reaches the maximum, which causes the device to resonate at the resonant frequency, with a large displacement and a high-amplitude peak and a small frequency domain bandwidth, which deteriorates the sound pressure level SPL (Sound Pressure Level) frequency response curve and the THD (Total Harmonic Distortion) frequency response curve, resulting in poor sound quality of the MEMS piezoelectric sounder. In addition, the MEMS piezoelectric sounder in the related art pushes a small amount of air, which reduces the output sound pressure level SPL of the MEMS piezoelectric sounder under excitation, and also affects the sound pressure level SPL frequency response curve. Utility Model Content

[0003] The purpose of the utility model is to provide a MEMS piezoelectric sounder and a loudspeaker to increase the sound pressure level, improve the sound pressure level SPL frequency response curve and the THD frequency response curve, and further improve the sound quality of the MEMS piezoelectric sounder.

[0004] The utility model provides a MEMS piezoelectric sounder, comprising: a substrate, wherein first piezoelectric composite layers are symmetrically arranged at a group of designated edge positions relative to each other on the upper surface of the substrate; each of the first piezoelectric composite layers is a rectangular structure; a cavity is provided in the bottom central area of ​​the substrate, and at least a portion of each of the first piezoelectric composite layers is located in the upper area of ​​the substrate corresponding to the cavity; in the upper area, a plurality of slotted structures are provided in designated areas other than at least a portion of each of the first piezoelectric composite layers, at least a portion of the slotted structures are covered with flexible materials, and the upper area with the flexible material forms a diaphragm structure of the MEMS piezoelectric sounder; the diaphragm structure is a rectangular bridge structure; the first diaphragm edge of the diaphragm structure is an anchoring edge, and the other diaphragm edges except the first diaphragm edge are non-anchoring edges; an edge slotted structure is provided at each of the non-anchoring edges, and the first diaphragm edge is determined according to the relative position of the first piezoelectric composite layer on the substrate.

[0005] Furthermore, the edge slot structures corresponding to the two opposite non-anchoring edges are parallel to each other, and the sizes of the edge slot structures are the same.

[0006] Furthermore, the diaphragm structure is parallel to the upper surface of the substrate, and at least a portion of the anchoring edge is fixed on the substrate.

[0007] Furthermore, at least one second piezoelectric composite layer is provided in the upper area of ​​the substrate; a groove structure is provided on each of the second piezoelectric composite layers, and / or a groove structure is provided in an area other than each of the second piezoelectric composite layers in the designated area; and the groove structure is covered with a flexible material.

[0008] Furthermore, the aspect ratio of the diaphragm structure is greater than a preset value; as the aspect ratio of the diaphragm structure increases, the value of the first-order resonant frequency of the MEMS piezoelectric sounder increases, and the difference between each order of resonant frequency decreases.

[0009] Furthermore, the thickness range of the diaphragm structure is 0.1 μm to 50 μm; as the thickness of the diaphragm structure is thinner, the value of the first-order resonance frequency is smaller, and under the same piezoelectric drive, the deflection displacement generated by the diaphragm structure is larger, and the amount of air pushed out is greater.

[0010] Furthermore, the larger the size of the cavity, the smaller the value of the first-order resonant frequency; wherein the size includes at least one of the following: the cavity area, cavity length, cavity width, cavity radius, and cavity diameter.

[0011] Furthermore, the neutral layer of the diaphragm structure is located at the center of the diaphragm structure.

[0012] Furthermore, each of the first piezoelectric composite layers and each of the second piezoelectric composite layers include, from bottom to top, a bottom electrode layer, an intermediate layer and a top electrode layer; wherein the intermediate layer is a piezoelectric layer, or the intermediate layer is formed by overlapping and stacking a plurality of piezoelectric layers and a plurality of electrode layers; wherein the upper layer of the bottom electrode layer and the lower layer of the top electrode layer are both piezoelectric layers.

[0013] The utility model provides a loudspeaker, comprising at least one MEMS piezoelectric sound generator according to any one of claims 1 to 9, wherein each MEMS piezoelectric sound generator is arranged in a preset array form.

[0014] The MEMS piezoelectric sounder and loudspeaker provided by the utility model include: a substrate, wherein first piezoelectric composite layers are symmetrically arranged at a group of designated edge positions relative to the upper surface of the substrate; each first piezoelectric composite layer is a rectangular structure; a cavity is provided in the bottom central area of ​​the substrate, and at least a part of each first piezoelectric composite layer is located in the upper area of ​​the substrate corresponding to the cavity; a plurality of slotted structures are provided in a designated area of ​​the upper area except at least a part of each first piezoelectric composite layer, at least a part of the slotted structures is covered with a flexible material, and the upper area with the flexible material forms a diaphragm structure of the MEMS piezoelectric sounder; the diaphragm structure is a rectangular bridge structure; the first diaphragm edge of the diaphragm structure corresponding to the first piezoelectric composite layer is an anchoring edge, and the other diaphragm edges except the first diaphragm edge are non-anchoring edges; an edge slotted structure is provided at each non-anchoring edge. By setting a slotted structure, the internal stress of each membrane layer in the diaphragm structure caused by the process can be reduced. By covering the slotted structure with a flexible material, the flexibility of the diaphragm structure can be improved, while reducing the sound leakage of the MEMS piezoelectric sounder at low frequencies, and improving the vibration amplitude and emission sound pressure level of the MEMS piezoelectric sounder. By replacing the high-density silicon diaphragm with a low-density flexible material, the mass of the diaphragm structure is reduced, and the diaphragm structure with a rectangular bridge structure can push out more air. The flexible material increases the damping of the system, which is beneficial to improving the sound pressure level SPL frequency response curve and the THD frequency response curve, thereby improving the sound quality of the MEMS piezoelectric sounder. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the specific implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0016] Figure 1 A schematic diagram of the structure of a MEMS piezoelectric sound generator provided in an embodiment of the utility model;

[0017] Figure 2 A schematic diagram of the structure of a MEMS piezoelectric sound generator provided in an embodiment of the utility model;

[0018] Figure 3(a) , 3(b) 3(c) is a schematic structural diagram of a piezoelectric composite unit provided in an embodiment of the utility model;

[0019] Figure 4(a) , 4(b), 4(c), 4(d), 4(e), 4(f), 4(g), 4(h), 4(i), 4(j), 4(k), 4(m), 4(n), 4(o), 4(p), 4(q), and 4(r) are schematic diagrams of the structure of a MEMS piezoelectric sounder provided in an embodiment of the present utility model;

[0020] Figure 5(a) , 5(b) , 5(c), 5(d) are schematic diagrams of polarization mode and electrical connection of a MEMS piezoelectric sound generator provided by an embodiment of the utility model;

[0021] Figure 6(a) , 6(b) 6(c) and 6(d) are schematic diagrams of simulation results of a MEMS piezoelectric sound generator provided by an embodiment of the utility model;

[0022] Figure 7(a) , 7(b) A schematic diagram of polarization mode and electrical connection of a MEMS piezoelectric sounder provided in an embodiment of the utility model;

[0023] Figure 8(a) , 8(b) , 8(c), 8(d) are schematic diagrams of polarization mode and electrical connection of a MEMS piezoelectric sound generator provided by an embodiment of the utility model;

[0024] Figure 9(a) , 9(b) A schematic diagram of polarization mode and electrical connection of a MEMS piezoelectric sounder provided in an embodiment of the utility model;

[0025] Figure 10(a) , 10(b) 10(c) is a schematic diagram of an array arrangement provided in an embodiment of the utility model;

[0026] Figure 11(a) , 11(b) , 11(c) is a schematic diagram of an array arrangement provided in an embodiment of the utility model;

[0027] Figure 12(a) , 12(b) A schematic diagram of an array arrangement provided by an embodiment of the utility model;

[0028] Figure 13(a) , 13(b) , 13(c), 13(d), 13(e), 13(f), 13(g), 13(h) are schematic diagrams of an array arrangement provided in an embodiment of the utility model;

[0029] FIG14( a) is a schematic diagram of a speaker provided in an embodiment of the present utility model;

[0030] Figure 14(b) , 14(c) A schematic diagram of simulation results provided for an embodiment of the utility model;

[0031] FIG15( a) is a schematic diagram of a speaker provided in an embodiment of the present utility model;

[0032] Figure 15(b) , 15(c) A schematic diagram of simulation results provided for an embodiment of the utility model;

[0033] Fig.16 A flowchart of a method for preparing a MEMS piezoelectric sound generator provided in an embodiment of the utility model;

[0034] Fig.17 A schematic cross-sectional view of a substrate having an insulating layer grown thereon provided in an embodiment of the utility model;

[0035] Fig.18 A schematic cross-sectional view of a bottom electrode layer after growth provided by an embodiment of the utility model;

[0036] Fig.19 A schematic cross-sectional view of a method of growing an intermediate layer and a top electrode layer provided in an embodiment of the utility model;

[0037] Fig. 20 A graphical cross-sectional schematic diagram provided for an embodiment of the utility model;

[0038] Fig.21 A schematic cross-sectional view of a passivation layer after deposition and patterning provided by an embodiment of the utility model;

[0039] Fig. 22 A schematic cross-sectional view of a metal wire after deposition and patterning provided by an embodiment of the utility model;

[0040] Fig.23 A schematic cross-sectional view of an SOI top silicon trench after etching provided by an embodiment of the utility model;

[0041] Fig.24 A schematic cross-sectional view of a device coated with a flexible film material provided in an embodiment of the utility model. DETAILED DESCRIPTION

[0042] The technical solution of the utility model will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0043] Most consumer electronic sound-generating devices use traditional electric types, which are composed of magnets, voice coils, diaphragms, support structures and shells. This working principle limits the minimum height that the sound-generating device can reach. To produce sound, an important factor is the effective diaphragm radiation area. The larger the area, the more air is output under the same thrust, and the louder the sound is. The second factor is the movement of the diaphragm radiation area: the greater the area of ​​the diaphragm is offset, the louder the sound is. In order to achieve small-sized, high-sound-pressure-level sound-generating devices, speakers, etc., the trend of MEMS sensors, speakers and transducers is to replace the entire system with silicone equivalents. Piezoelectric MEMS sound-generating devices manufactured based on MEMS technology use piezoelectric film materials as actuators. Piezoelectric MEMS speakers have become a research hotspot due to their small size, low power consumption, low cost, and batch manufacturing capabilities.

[0044] Silicon processing results in an inherently thin form factor, with the MEMS motor in the speaker being less than half a millimeter thick, an order of magnitude thinner than an electric speaker. MEMS speakers benefit from the stabilizing effect of the piezoelectric motor, which not only provides the driving force but also makes the motion more linear and controllable. The linear actuator of the piezoelectric MEMS sound-generating device has higher speed and precision than the voice coil, resulting in higher bandwidth and more accurate high-frequency reproduction.

[0045] The related art provides a sound-emitting unit and a manufacturing method thereof, wherein the sound-emitting unit includes a diaphragm and an actuating layer. The diaphragm includes a first diaphragm sub-portion and a second diaphragm sub-portion, the first diaphragm sub-portion and the second diaphragm sub-portion are opposite to each other, and the actuating layer is arranged on the first diaphragm sub-portion and the second diaphragm sub-portion. The first diaphragm sub-portion includes a first anchoring edge, the first anchoring edge is fully anchored or partially anchored, and the edges of the first diaphragm sub-portion except the first anchoring edge are all non-anchored. The second diaphragm sub-portion includes a second anchoring edge, the second anchoring edge is fully anchored or partially anchored, and the edges of the second diaphragm sub-portion except the second anchoring edge are all non-anchored. However, due to the process and the stress limitation of each layer structure, this method will lead to large harmonic distortion (THD), and the ability to improve the sound pressure level (SPL) is also limited; the slotted cantilever beam structure is prone to air leakage.

[0046] The related art also provides a micro-electromechanical sound transducer with a polymer coating, which forms a cured polymer after the polymer has been cured, which has another advantage. The coating formed by the cured polymer and the piezoelectric component form a composite structure. The piezoelectric component can be formed of ceramics, for example. In addition, if the piezoelectric component is relatively thin, the vibration performance of the piezoelectric component is better. However, this increases the risk of cracking the piezoelectric component. The piezoelectric component can be stabilized by a coating formed by a cured polymer, which is elastic and flexible even after curing. The coating made of a cured polymer and the piezoelectric component form a composite system, so that the piezoelectric component is stabilized by the coating. However, in this method, the coating formed by the cured polymer only acts as a protective structure and does not reduce the quality of the vibrating film. The coating formed by the cured polymer and the piezoelectric component form a composite structure, which will cause greater harmonic distortion (THD) due to the process and the stress limitations of each layer structure, and the ability to increase the sound pressure level (SPL) is also limited.

[0047] In summary, in the related art, the system damping of the piezoelectric MEMS sound unit is small, the quality factor of the device resonance is large, and the displacement of the piezoelectric MEMS sound unit at the resonant frequency reaches the maximum, which causes the device to resonate at the resonant frequency, with a large displacement and a high-amplitude peak and a small frequency domain bandwidth, which deteriorates the sound pressure level SPL frequency response curve and the THD frequency response curve, resulting in poor sound quality of the piezoelectric MEMS sound unit. In a small-sized square or circular structure, due to the high symmetry of the structure, the modes excited by the square or circular diaphragm are both odd mode and even mode. In the even mode state, the vibrations of the diaphragm under excitation cancel each other out, resulting in a lower output sound pressure level SPL, which also affects the sound pressure level SPL frequency response curve. Based on this, the embodiment of the utility model provides a piezoelectric MEMS sound unit and a speaker, and the technology can be applied to applications that need to improve the sound quality of the piezoelectric MEMS sound unit.

[0048] To facilitate understanding of the present embodiment, a MEMS piezoelectric sounder disclosed in an embodiment of the present utility model is first introduced, and the MEMS piezoelectric generator includes: a substrate, and first piezoelectric composite layers are symmetrically arranged at a set of designated edge positions relative to each other on the upper surface of the substrate; each first piezoelectric composite layer is a rectangular structure; the bottom central area of ​​the substrate has a cavity, and at least a portion of each first piezoelectric composite layer is located in the upper area of ​​the substrate corresponding to the cavity; in the upper area, a designated area other than at least a portion of each first piezoelectric composite layer is provided with a plurality of slotted structures, at least a portion of the slotted structures is covered with a flexible material, and the upper area with the flexible material forms a diaphragm structure of the MEMS piezoelectric sounder; the diaphragm structure is a rectangular bridge structure; the first diaphragm edge of the diaphragm structure is an anchoring edge, and the other diaphragm edges except the first diaphragm edge are non-anchoring edges; an edge slot structure is respectively provided at each non-anchoring edge, and the first diaphragm edge is determined according to the relative position of the first piezoelectric composite layer on the substrate.

[0049] The material of the substrate can also be selected from SOI (Silicon-On-Insulator, i.e., silicon on an insulating substrate), silicon, glass, sapphire, etc., and can be selected according to actual needs; the upper surface of the substrate is usually covered with an insulating layer, and the substrate usually has multiple edge positions. For example, if the upper surface of the substrate is a rectangle, it includes two opposite groups of edge positions; the above-mentioned designated edge positions can be any group of edge positions, and preferably, the designated edge positions are a group of edge positions corresponding to two opposite long sides of the rectangle; the first piezoelectric composite layers are symmetrically arranged at the group of designated edge positions, that is, the first piezoelectric composite layers arranged at each edge position in the group of designated edge positions are relative to each other. , and each first piezoelectric composite layer is a rectangular structure; the MEMS piezoelectric sounder can perform electroacoustic conversion through the first piezoelectric composite layer, and a driving signal is applied to the first piezoelectric composite layer. The first piezoelectric composite layer can deform the diaphragm structure under the drive of the electrical signal, thereby generating sound waves and realizing the vibration sound of the MEMS piezoelectric sounder; the size and shape of the above-mentioned cavity can be set according to actual needs, and the back side of the substrate can be etched to form the above-mentioned cavity. By designing cavity structures of different sizes, the resonant frequency of the MEMS piezoelectric sounder can be changed, so that it can be applied to speakers or ultrasonic transducers, etc. Usually, different cavity sizes will result in different first-order resonant frequencies of the MEMS piezoelectric sounder.

[0050] A positive projection is made from the cavity to the upper surface of the substrate, and the area corresponding to the projection is the upper area of ​​the substrate. A part of each first piezoelectric composite layer is located in the upper area. In the range of the upper area, a designated area other than a part of each first piezoelectric composite layer is provided with a plurality of slotted structures, and the designated area may include: a middle rectangular area and / or an edge position of the substrate, etc.; the shape and number of the slotted structures can be set according to actual needs. The above-mentioned flexible material can be selected from dry films, for example, one of the following materials can be selected but not limited to: polyimide, polyparaxylene, polyurethane, PVI-3 (PVI English full name Poly Vinyl Isobutyl ether, vinyl isobutyl ether), photosensitive cover film Flexfiner SA or other organic films; the thickness of the flexible material film layer is usually between 0.5μm and 30μm, preferably, the thickness can be selected to be 5μm, the flexible material can not only cover the slotted structure, but also act as a diaphragm, and can also be used as an insulating layer material to cover the metal connection, playing the role of electrical insulation and waterproofing. When the flexible material covers at least a portion of the slotted structure, the length and width of the flexible material covered are generally larger than the length and width of the slotted structure.

[0051] The above-mentioned flexible materials are usually required to have the following properties: compatible with MEMS processes, graphable, long-term operation, anti-aging, and good mechanical and temperature stability. In addition, the flexible material needs to have a certain stretchability, and the difference in thermal expansion coefficient between the flexible material and the substrate can minimize the wafer bending.

[0052] The upper area of ​​the substrate with flexible material forms a diaphragm structure of the MEMS piezoelectric sounder. The diaphragm can be a hard substrate or a flexible substrate. The material can be single crystal silicon, polycrystalline silicon, glass, polymer (for example, polyimide (PI), polyethylene terephthalate (PET), organic or inorganic compound, any suitable material or a combination thereof.

[0053] The above-mentioned diaphragm structure is a rectangular bridge structure, and the first diaphragm edge of the diaphragm structure is an anchoring edge. For example, the two long sides of the diaphragm structure are anchoring edges, and the two short sides of the diaphragm structure are non-anchoring edges; an edge groove structure is respectively arranged on each non-anchoring edge, and the first diaphragm edge is determined according to the relative position of the first piezoelectric composite layer on the substrate. For example, if the first piezoelectric composite layer is on the left side of the substrate, the left diaphragm edge of the diaphragm structure is the anchoring edge, and if the first piezoelectric composite layer is on the right side of the substrate, the right diaphragm edge of the diaphragm structure is the anchoring edge.

[0054] like Figure 1A structural schematic diagram of a MEMS piezoelectric sounder is shown, which takes the substrate made of SOI material as an example for explanation, including: SOI base silicon 01, BOX layer silicon dioxide barrier layer 02, SOI top silicon 03; an insulating layer 04 formed on the SOI top silicon 03, a seed layer 05 formed on the insulating layer 04, a bottom electrode layer 06, an intermediate electrode layer 07 and a top electrode layer 08 of the first piezoelectric composite layer, a bottom piezoelectric layer 09 and a top piezoelectric layer 10 of the first piezoelectric composite layer; a groove 16 etched on the SOI top silicon 03 is a linear groove, and the groove 16 is located above the hollow area of ​​the device cavity 15. The groove 16 can be obtained by a DRIE (Deep Reactive Ion Etching) process, and the width of the groove 16 is usually designed to be 0.5μm to 2000μm, which decouples the device structure and releases the process internal stress of each membrane layer, thereby obtaining a larger driving displacement and sound pressure level output. The flexible material 17 covers the groove 16, and its width is greater than that of the etched groove 16, which can prevent sound leakage; 11 is the diaphragm of the device, which is composed of SOI top silicon 03 and the first piezoelectric composite layer, and is the sound-generating part of the MEMS piezoelectric sounder. The insulating layer 14 can play the role of electrical insulation and isolation protection, and the welding pads 12 and 13 are both connection points of the signal input terminal, and can be connected to the first piezoelectric composite layer of the MEMS piezoelectric sounder through metal wires.

[0055] like Figure 2 A schematic diagram of the structure of a MEMS piezoelectric sounder is shown, wherein: Figure 1 Equivalent to Figure 2 Corresponding cross-sectional views, it should be noted that the term "left and right" refers to the two sides of the MEMS piezoelectric sounder substantially along the X-axis direction, "up and down" refers to the two sides along the Y-axis direction, and "inside and outside" refers to the two sides along the Z-axis direction. Moving downward means that the MEMS piezoelectric sounder substantially moves along the Y-axis direction.

[0056] like Figure 2As shown, the MEMS piezoelectric sounder D10 includes a diaphragm structure, and left and right first piezoelectric composite layers 10a and 10b of the diaphragm structure, and a middle second piezoelectric composite layer 10c. The two first piezoelectric composite layers are separated from each other, are rectangular structures, and are arranged on the diaphragm structure, wherein the left and right first piezoelectric composite layers 10a and 10b are respectively connected to the edges 30a and 30c anchored to the device, and are fixed on the substrate of the device, exceeding the cavity edges 20a and 20c on the back of the device, and the inner edges of the first piezoelectric composite layers 10a and 10b are 60a and 60b, and the two edges are parallel to each other and symmetrical about the Y axis. The thin dotted lines 20a, 20b, 20c, and 20d in the figure form a rectangle, which is the cavity area on the back of the device, obtained by back etching process or other methods, so that the diaphragm structure vibrates on the device and deviates. The MEMS piezoelectric sounder D10 has a plurality of slotted structures, namely the white dotted lines 40a, 40b, 40c, and 40d in the figure. The slotted structures 40a and 40b are on the upper and lower sides of the diaphragm structure, dividing the device at the edges 30b and 30d. The shape of the diaphragm structure is a rectangular bridge structure, or a rectangular cantilever beam structure, or a shape with a slit or other suitable shapes, or at least one or more straight line patterns, or other pattern combinations, etc. The slotted structures 40c and 40d are on both sides of the second piezoelectric composite layer 10c in the middle of the diaphragm, and may be one or more straight line patterns, or other pattern combinations such as curved curves. The slotted structures 40c and 40d are covered with flexible materials 70a and 70b, and the slotted structures 40a and 40b may not be covered. The length and width of the flexible material are usually larger than the length and width of the slotted structure, that is, full coverage. Of course, the length may not be completely covered, or multiple sections of flexible materials may be used to not completely cover the slotted structures 40c and 40d. When the slotted structure is covered by a flexible material, the slotted size can be very large, and can be 2000 μm in length, width, diameter and other dimensional parameters.

[0057] The above-mentioned MEMS piezoelectric sounder can reduce the internal stress of each membrane layer in the diaphragm structure caused by the process by setting a slotted structure. The slotted structure is covered with a flexible material, which can improve the flexibility of the diaphragm structure and reduce the sound leakage of the MEMS piezoelectric sounder at low frequencies. The vibration amplitude and emission sound pressure level of the MEMS piezoelectric sounder are improved. By replacing the silicon diaphragm with a higher density with a low-density flexible material, the mass of the diaphragm structure is reduced, and the diaphragm structure with a rectangular bridge structure can push out more air. The flexible material increases the damping of the system, which is beneficial to improving the sound pressure level SPL frequency response curve and the THD frequency response curve, thereby improving the sound quality of the MEMS piezoelectric sounder.

[0058] Furthermore, the edge slot structures corresponding to the two opposite non-anchoring edges are parallel to each other, and the sizes of the edge slot structures are the same.

[0059] In actual implementation, Figure 2 As shown, the two short sides of the diaphragm structure are non-anchored edges, which can also be called free edges. The free edges are generally slotted to form free ends through process technology. The slotted structures 40a and 40b on the upper and lower sides correspond to the above-mentioned edge slotted structures. The slotted structures 40a and 40b are generally the same in size and parallel to each other. The slotted structures 40a and 40b may also not be completely slotted.

[0060] The upper and lower sides of the diaphragm structure both include slotted structures. For example, on the left side of the diaphragm structure, the slotted structures are formed on the other three edges of the diaphragm structure except the anchoring edge. The three slotted structures corresponding to the other three edges constitute the free end of the left side of the diaphragm structure. The anchoring edge on the left side of the diaphragm structure is at the same position as the anchoring edge on the right side of the diaphragm structure and is fixed on the substrate of the device.

[0061] Furthermore, the diaphragm structure is parallel to the upper surface of the substrate, and at least a portion of the anchoring edge is fixed on the substrate.

[0062] The diaphragm structure is usually parallel to the upper surface of the substrate, and the anchoring edge can be completely fixed on the substrate or partially fixed on the substrate.

[0063] Furthermore, at least one second piezoelectric composite layer is provided in the upper region of the substrate; a groove structure is provided on each second piezoelectric composite layer, and / or a groove structure is provided in a designated region except for each second piezoelectric composite layer; and the groove structure is covered with a flexible material.

[0064] One or more second piezoelectric composite layers may be disposed in the middle of the upper region of the substrate, which may also be understood as one or more second piezoelectric composite layers may be disposed in the middle of the diaphragm structure of the MEMS piezoelectric sounder. Figure 1 and Figure 2 As shown, the middle second piezoelectric composite layer 10c is separated from the second piezoelectric composite layer 10a and the second piezoelectric composite layer 10b, and all of them are rectangular structures, and are arranged on the diaphragm structure; a groove structure can be arranged on each second piezoelectric composite layer, and a groove structure can also be arranged around the second piezoelectric composite layer in a specified area, such as Figure 2 40c and 40d in the figure can be selected according to actual needs, and the slotted structure is covered with a flexible material, and the length and width of the covering material are usually larger than the length and width of the slotted structure. In actual implementation, the second piezoelectric composite layer in the central area can also be divided into two or more parts, and the shapes can be circular, hexagonal, octagonal or other irregular graphic structures. The internal stress can be released through the slotted structure, for example, Figure 2In the figure, the slotted structure can release the internal stress generated in the process of manufacturing the diaphragm structure 50a, 50b area and the first piezoelectric composite layer and the second piezoelectric composite layer. The width of the slotted structure should be small enough. The slotted structure in the figure is generally less than 10μm wide.

[0065] In actual implementation, the slotted structure may run through the entire diaphragm structure, dividing the diaphragm structure into two parts to form a cantilever beam structure, or a portion may be left to form a connecting lock structure, so that the diaphragm structure vibrates uniformly when driven.

[0066] When the width of the slotted structure is relatively small, it is necessary to penetrate the diaphragm structure in the thickness direction, that is, the thickness of the diaphragm structure. When the width of the slotted structure is greater than 5μm, it is necessary to cover it with a flexible material, which is helpful to prevent sound leakage. When the width of the slotted structure is less than 5μm, the diaphragm structure vibrates and makes a sound. When the sound propagates in a narrow slit, heat loss and viscous loss will cause the sound wave to attenuate. It does not need to be covered with a flexible material, and it will not cause large sound losses at low frequencies.

[0067] When the slot structure is relatively large in width, it penetrates the diaphragm structure in the thickness direction and is the thickness of the diaphragm structure. When the slot structure is 5μm-2000μm wide, the diaphragm structure formed in combination with the rigid material can improve the flexibility of the diaphragm structure and seal the airflow, so that there is no leakage area in the MEMS piezoelectric sounder, reduce the sound leakage of the MEMS piezoelectric sounder at low frequencies, and increase the vibration amplitude and emission sound pressure level of the piezoelectric MEMS generating unit. When the slot structure is relatively large in size, the mass of the diaphragm structure can be reduced, which is conducive to improving the sound pressure level curve and improving the mid-frequency performance.

[0068] The quality factor Q of the resonance of the MEMS piezoelectric sounder is usually relatively large, and after the excitation is applied, the displacement frequency curve or the sound pressure level frequency curve has a sharp peak and a narrow peak frequency response. Therefore, this embodiment uses a flexible material to form a rigid-flexible diaphragm structure, which can increase the system damping to reduce the quality factor Q of its resonance, thereby making the sound pressure level curve flat and reducing the total harmonic interference THD.

[0069] Furthermore, the aspect ratio of the diaphragm structure is greater than a preset value; as the aspect ratio of the diaphragm structure increases, the value of the first-order resonant frequency of the MEMS piezoelectric sounder increases, and the difference between each order of resonant frequency decreases.

[0070] In the present embodiment, the diaphragm structure is a rectangular bridge structure. For example, the anchoring edges on the left and right sides are the length of the diaphragm structure, while the non-anchoring edges on the upper and lower sides are the width of the diaphragm structure. The aspect ratio is greater than a preset threshold, such as greater than or equal to 3. The cavity size, the size of the diaphragm structure, and the thickness of the diaphragm structure of the MEMS piezoelectric sounder are closely related to the resonant frequency of the MEMS piezoelectric sounder. The length and width of the rectangular diaphragm structure will affect the resonant frequency of the MEMS piezoelectric sounder, wherein the smaller the diaphragm width, the higher the resonant frequency can be obtained. The diaphragm length of the MEMS piezoelectric sounder affects the output sound pressure level of the device. A MEMS piezoelectric sounder with a large aspect ratio can achieve a higher resonant frequency and a larger sound pressure level than a MEMS piezoelectric sounder with a small aspect ratio. Figure 2 Taking the MEMS piezoelectric sounder D10 in the example, the aspect ratio of the diaphragm structure of the MEMS piezoelectric sounder D10 can be greater than 3 or other. The larger the aspect ratio of the diaphragm structure, the larger the value of the first-order resonant frequency of the MEMS piezoelectric sounder, and the smaller the difference between the resonance frequencies of each order. When the quality factor Q of the resonance of the MEMS piezoelectric sounder D10 is reduced, the resonance can be mixed. By using multiple MEMS piezoelectric sounders D10 to form an array structure, multiple relatively wide-band smooth peaks can be mixed together to form a frequency response that is relatively flat to the resonance frequency, thereby improving the performance of the MEMS piezoelectric sounder D10.

[0071] By applying a drive to the first piezoelectric composite layer 10a, 10b, the diaphragm structure is displaced and deflected to move along the Z-axis direction, thereby pushing the air to make a sound and converting mechanical acoustic energy. It should be noted that the audio drive signal applied to the first piezoelectric composite layer corresponds to the output sound wave signal, corresponding to the input drive signal. The audio drive signal is generally a sinusoidal signal of a DC voltage plus an AC voltage, such as 10VDV+10VP; or driven by a bipolar signal. The diaphragm structure of the MEMS piezoelectric sounder D10 is a rectangular bridge structure, such as Figure 2 As shown, the length direction of the diaphragm structure is the anchoring edge, and the width direction is the non-anchoring edge. The width of the diaphragm structure significantly affects the first-order resonant frequency of the MEMS piezoelectric sounder D10, while the length of the diaphragm structure has little effect on the resonant frequency, but has a great influence on the amount of air pushed by the diaphragm under excitation. Therefore, the length-to-width ratio is generally large in the structural design of the MEMS piezoelectric sounder.

[0072] Furthermore, the thickness range of the diaphragm structure is 0.1 μm to 50 μm; as the thickness of the diaphragm structure is thinner, the value of the first-order resonance frequency is smaller, and under the same piezoelectric drive, the deflection displacement generated by the diaphragm structure is larger, and the amount of air pushed out is larger.

[0073] In this embodiment, the thickness range of the diaphragm structure is 0.1μm to 50μm; the thickness may vary. Generally speaking, it is preferably between 1μm and 5μm, which needs to be determined according to the size and performance parameters of the MEMS piezoelectric sounder design. For example, when the MEMS piezoelectric sounder and the cavity size are determined, if the first-order resonant frequency of the MEMS piezoelectric sounder is required to be lower, a diaphragm structure with a thinner thickness is usually selected. If the first-order resonant frequency of the MEMS piezoelectric sounder is required to be higher, a diaphragm structure with a thicker thickness is usually selected. The first-order resonant frequency of the MEMS piezoelectric sounder is not only related to the stiffness of the diaphragm structure, but also to the mass of the diaphragm structure. When the parameters such as the cavity size of the MEMS piezoelectric sounder are certain, generally speaking, the thinner the thickness of the diaphragm structure, the lower the first-order resonant frequency of the MEMS piezoelectric sounder. When the MEMS piezoelectric sounder and the size of the cavity of the MEMS piezoelectric sounder are determined, the resonant frequency can be adjusted by changing the thickness of the diaphragm structure. At this time, the thinner the thickness of the diaphragm structure is, the lower the first-order resonant frequency and stiffness of the MEMS piezoelectric sounder are. Under the same piezoelectric drive, the greater the deflection displacement produced by the diaphragm structure, the greater the amount of air pushed out, and the higher the output sound pressure level.

[0074] Furthermore, the larger the size of the cavity, the smaller the value of the first-order resonant frequency; wherein the size includes at least one of the following: cavity area, cavity length, cavity width, cavity radius, and cavity diameter.

[0075] The shape of the above-mentioned cavity can be set according to actual needs. For example, from the top view or bottom view of the MEMS piezoelectric sounder, the shape of the cavity can be rectangular, circular or other shapes. Generally, the larger the size of the cavity, the lower the first-order resonant frequency of the MEMS piezoelectric sounder. The size here can refer to measurement parameters such as cavity area, cavity length, cavity width, cavity radius or cavity diameter.

[0076] Furthermore, the neutral layer of the diaphragm structure is located at the center of the diaphragm structure.

[0077] The neutral layer of the entire diaphragm structure of the MEMS piezoelectric sounder is designed in the center of the diaphragm structure, which is conducive to the opposite forces (tension and pressure) of the upper and lower piezoelectric composite layers of the diaphragm structure. Through reasonable electrical connection and application of appropriate drive, the output sound pressure level of the device can be improved. The above-mentioned neutral layer refers to the stress neutral layer. For example, the outer layer of the diaphragm structure is subjected to tensile stress, while the inner layer is subjected to compressive stress. Between the tensile stress and the compressive stress, there is always a point where the stress is zero. This layer with zero stress is the stress neutral layer. When making electrical connections, it is necessary to consider the number of piezoelectric layers and the polarization direction of each part of the piezoelectric layer, so as to make electrical connections so that the output sound pressure level of the piezoelectric MEMS generating unit is maximized. The drive is generally an electrical signal composed of a DC plus an AC voltage. Generally, the AC voltage does not exceed 30VP, and the DC voltage generally does not exceed 15V.

[0078] Furthermore, each first piezoelectric composite layer and each second piezoelectric composite layer include, from bottom to top, a bottom electrode layer, an intermediate layer and a top electrode layer; wherein the intermediate layer is a piezoelectric layer, or the intermediate layer is formed by overlapping and stacking multiple piezoelectric layers and multiple electrode layers; wherein the upper layer of the bottom electrode layer and the lower layer of the top electrode layer are both piezoelectric layers.

[0079] Each of the above-mentioned first piezoelectric composite layers and each of the second piezoelectric composite layers can be a single piezoelectric layer structure, that is, electrode layer / piezoelectric layer / electrode layer; it can be a double piezoelectric layer structure: electrode layer / piezoelectric layer / electrode layer / piezoelectric layer / electrode layer, and a multi-piezoelectric layer structure: electrode layer / piezoelectric layer / electrode layer... / piezoelectric layer / electrode layer; the appropriate structure can be selected according to actual needs.

[0080] As shown in Fig. 3(a), there is a schematic diagram of the structure of a piezoelectric composite layer, as shown in Fig. 3(b), and as shown in Fig. 3(c), there is a schematic diagram of the structure of a piezoelectric composite layer, wherein the piezoelectric composite layer in Fig. 3(a) is a single piezoelectric layer, and the piezoelectric composite layers are respectively bottom electrode layer, piezoelectric layer, and top electrode layer from bottom to top; the piezoelectric composite layer in Fig. 3(b) is a double piezoelectric layer, and the piezoelectric composite layers are respectively bottom electrode layer, piezoelectric layer, electrode layer, piezoelectric layer, and top electrode layer from bottom to top; the piezoelectric composite layer in Fig. 3(c) is a multi-piezoelectric layer structure, and the multi-piezoelectric layer structure can be deduced in turn, which will not be described in detail here. According to the number of piezoelectric layers and the polarization direction of piezoelectric layers in different regions, there are a variety of electrical connection methods, and by comparison, the optimal connection method that maximizes the offset of the diaphragm structure of the MEMS piezoelectric sounder and outputs the highest sound pressure level can be obtained.

[0081] If the first piezoelectric composite layer and / or the second piezoelectric composite layer includes multiple piezoelectric layers, the material of each piezoelectric layer can be the same material or different materials, the thickness of different piezoelectric layers can be the same or different, and the thickness range of the piezoelectric layer is usually between 0.1μm and 25μm. The appropriate material or thickness can be selected according to actual needs. The material of the piezoelectric layer can be a single crystal piezoelectric material or a polycrystalline material, for example: single crystal AlN, doped AlN, single crystal PZT, doped PZT, ZnO and other piezoelectric materials.

[0082] Similarly, if the first piezoelectric composite layer and / or the second piezoelectric composite layer includes multiple electrode layers, the material of each electrode layer can be the same material or different materials, the thickness of different electrode layers can be the same or different, and the thickness range of the electrode layer is usually between 0.01 μm and 5 μm. The appropriate material or thickness can be selected according to actual needs. The material of the electrode layer can be a single crystal metal material such as Mo, Pt, Al, Cu, or the same material as an alloy material.

[0083] Figure 1 and Figure 2 The MEMS piezoelectric sounder includes a diaphragm structure, which is a rectangular bridge structure, including: a first piezoelectric composite layer on the left and right sides of the diaphragm structure, and a second piezoelectric composite layer in the middle. Each first piezoelectric composite layer and each second piezoelectric composite layer include: a double piezoelectric layer thin film structure of a bottom electrode layer, a lower piezoelectric layer, a middle electrode layer, an upper piezoelectric layer, and a top electrode layer located on the upper side of the diaphragm structure; one side edge of the first piezoelectric composite layer unit on the left and right sides is anchored on the device, and the other side edge is located on the diaphragm structure. The left and right sides of the diaphragm structure are anchored edges, and the upper and lower sides of the diaphragm structure are free edges, that is, non-anchored edges. The anchored edges are completely or partially fixed on the device substrate, and the free edges are generally grooved to form free ends through process technology.

[0084] In actual implementation, in addition to Figure 1 The diaphragm structure in the MEMS piezoelectric sounder can also be formed in other forms. For example, FIG4(a) shows a schematic diagram of the structure of a MEMS piezoelectric sounder. The MEMS piezoelectric sounder D11 is relatively Figure 2For the MEMS piezoelectric sounder D10 in the figure, the second piezoelectric composite layer inside the diaphragm structure of the MEMS piezoelectric sounder has three areas 10c, 10d, and 10e. The diaphragm structure near each second piezoelectric composite layer has a slotted structure 40c, 40d, and the slotted structures 40c, 40d are covered with flexible materials 70a, 70b. The three second piezoelectric composite layers 10c, 10d, and 10e in the figure can be equal in size (length), and the edges of the three second piezoelectric composite layers are parallel to each other and symmetrical about the horizontal axis X direction and the vertical axis Y direction. Of course, it can also be designed that the three second piezoelectric composite layers are of different sizes, or other structural forms in which any two of them are equal.

[0085] As shown in FIG4(b), there are two second piezoelectric composite layers in the center of the diaphragm structure of the MEMS piezoelectric sounder D12. There is a diaphragm structure between the two second piezoelectric composite layers. L-shaped slot structures 40a and 40b are etched on the diaphragm and covered with flexible materials 70a and 70b. The size (length) can be equal and the unit edges are parallel to each other. The slot structure is located on the diaphragm near the piezoelectric composite layer and is symmetrical about the horizontal axis X direction and the vertical axis Y direction, and is covered with a flexible material.

[0086] As shown in FIG4(c), a schematic diagram of the structure of a MEMS piezoelectric sounder, the second piezoelectric composite layer inside the diaphragm of the MEMS piezoelectric sounder D13 is grooved, namely, the grooved structures 40c and 40d. The grooved structures 40c and 40d are not connected to each other and do not divide the second piezoelectric composite layer. And the flexible materials 70a and 70b are used for covering. The lengths of the grooved structure and the flexible material covered are equal and symmetrical along the longitudinal axis Y direction. Of course, it can also be designed that the lengths of the grooved structure and the flexible material covered are unequal and / or asymmetric. In FIG4(c), the grooved straight line can also extend to the diaphragm structure, respectively connected to the grooved structures 40a and 40b, and a grooved structure is synthesized to divide 10c into two areas. The grooved structure can also be composed of multiple line segments, and the length of the flexible material covered can be greater than and / or less than the length of the grooved structure.

[0087] As shown in Figure 4(d), a structural schematic diagram of a MEMS piezoelectric sounder is shown. Compared with the MEMS piezoelectric sounder D10, the MEMS piezoelectric sounder D14 does not have a second piezoelectric composite layer inside the diaphragm of the MEMS piezoelectric sounder, and the grooves 40c, 40d, and 40e are located on the central diaphragm of the device and are covered with flexible materials 70a, 70b, and 70c. The groove gap and the flexible material covering are located at the center of the diaphragm and are symmetrical about the horizontal axis X direction.

[0088] The above-mentioned MEMS piezoelectric sounder can be grooved on the second piezoelectric composite layer inside the diaphragm, as shown in Figure 4(c); it can also be grooved on the diaphragm, as shown in Figure 4(d), and the position of the groove is not limited to that shown in the figure; it can constitute a flexible diaphragm, and / or a vibrating film in which rigid and flexible materials are combined with each other.

[0089] For the above-mentioned piezoelectric MEMS piezoelectric sound unit, when the width dimension of the slotted structure is between 0.5μm and 5μm, its etching pattern can be a straight line, a circular line, a square line or other polygons and / or a combination of patterns; when the width dimension of the slotted structure is between 10μm and 200μm, its etching pattern can be a rectangle, a circle, a ring, a hexagon or other polygons and / or a combination of patterns, which can constitute a flexible diaphragm, and / or a vibrating film in which rigid and flexible materials are combined with each other.

[0090] As shown in FIG4(e), a schematic diagram of the structure of a MEMS piezoelectric sounder is shown. Compared with the MEMS piezoelectric sounder D10, the MEMS piezoelectric sounder D15 has no slotted structures or flexible material covering on both sides of the second piezoelectric composite layer inside the diaphragm, but has two slotted structures 40c and 40d on the second piezoelectric composite layer 10c in the middle of the diaphragm, and the gap is not covered with flexible material. The two slotted structures are of equal length, located on the diaphragm and rotationally symmetrical about the horizontal axis X direction. The slotted structures 40c and 40d can also be designed to be asymmetric and have different lengths. There can be one or more slotted structures 40c and 40d on the second piezoelectric composite layer 10c, and one slot can extend to the upper and lower slots 40a and 40b of the device, dividing the center of the device diaphragm into two cantilever beam structures, and the middle second piezoelectric composite layer 10c is divided into two regions.

[0091] As shown in FIG4(f), a schematic diagram of the structure of a MEMS piezoelectric sounder is shown, MEMS piezoelectric sounder D16, the second piezoelectric composite layer 10b, 10c, 10d inside the diaphragm, the slotted structures 40c, 40d are located inside the diaphragm of the device, and are symmetrical about the center horizontal line of the device. Compared with the MEMS piezoelectric sounder D15, the position of the slotted structure inside the diaphragm is different, and there are two slotted structures and they are centrally symmetrical, and the slotted structure is not covered with a flexible material. In actual implementation, the position of the slotted structure inside the diaphragm can be different, and the number of slotted structures can be multiple, which can be centrally symmetrical or not centrally symmetrical, and the slotted structure can be fully or partially covered with a flexible material or not.

[0092] As shown in FIG. 4( g ), a schematic diagram of the structure of a MEMS piezoelectric sounder, there are two second piezoelectric composite layers 10 c and 10 d inside the diaphragm structure of the MEMS piezoelectric sounder D17 , and no flexible material covers the slotted structure.

[0093] As shown in FIG4(h) , there is no second piezoelectric composite layer inside the diaphragm structure of the MEMS piezoelectric sounder D18, but there are three slotted structures 40c, 40d, and 40e. The slotted structure may be in the shape of a straight line, a circle, an annular shape, or a special shape, and the etching position, the number of etching slits, the size parameters of the etching slits (width, length, radius), etc. may have a variety of different structures or combined structures.

[0094] As shown in FIG4(i), a schematic diagram of the structure of a MEMS piezoelectric sounder is shown. The MEMS piezoelectric sounder D19 is different from the MEMS piezoelectric sounder D18. The slot structure is inside the diaphragm, and there are two slot structures 40c and 40d that are parallel and equal in length. The two slot structures 40c and 40d extend to the slot structures 40a and 40b, thereby connecting to form a rectangular structure. Through the MEMS process, the rectangular part can be completely removed, and the entire etched area is covered with a flexible material 70a. The size of the flexible material 70a is usually larger than the size of the etched rectangular groove. The left and right edges of the flexible material 70a exceed the slot structures 40c and 40d, but do not cover the first piezoelectric composite layers 10a and 10b on both sides of the middle of the diaphragm. Of course, during the design, the flexible material 70a can cover the first piezoelectric composite layers 10a and 10b on both sides of the middle of the diaphragm, so that the flexible material 70a is located on the piezoelectric composite layers 10a and 10b. At the same time, the entire area can be covered, and the flexible material 70a can be covered on the device frame 30a and 30b, or multiple sections of flexible materials can be covered in equal or unequal sections. The structural form of the flexible material 70a is various, and the structural size and distribution position are not limited to the device D19. The entire etched area is covered with a flexible material, and the size of the flexible material is larger than the size of the removed area. When the cavity of the device substrate is released, a rigid-flexible diaphragm can be formed. When the device vibrates, there is no air leakage inside the diaphragm. Using flexible materials for covering, removing the silicon diaphragm with a higher density, and using low-density flexible materials to replace the diaphragm structure, reducing the mass of the diaphragm is conducive to improving the sound pressure level curve and improving the mid-frequency performance. The etching shape of the center of the diaphragm can be a variety of structures, such as two rectangular frame structures, or circular, square, or polygonal structures. The number and position of the etched groove structures can be various and are not limited to those shown in device D19.

[0095] As shown in FIG4(j), there is a schematic diagram of the structure of a MEMS piezoelectric sounder. The piezoelectric MEMS piezoelectric sound unit D20 has six rectangular strip structure graphics 70b, 70c, 70d, 70e, 70f, and 70g made of flexible materials inside the diaphragm, compared with the piezoelectric MEMS piezoelectric sound unit D19. The six rectangular structures are of the same size and are regularly distributed inside the diaphragm, presenting a symmetrical structure on the horizontal and vertical axes. One side of the six flexible rectangular strips is located on the device D20 frame 30a, 30c, and the other side is connected to the rectangular frame formed by the middle flexible material 70a. The structure composed of flexible materials mainly acts as a reinforcing rib. Under piezoelectric drive, the resonant frequency of the device can be increased without significantly reducing the maximum deviation of the diaphragm, thereby widening the bandwidth of the device. The reinforcing rib structure composed of flexible materials is not limited to this, and its structure is diverse. Si material is relatively brittle. The diaphragm combined with PZT film and Si film layer is used for the anchoring position of the driver, which may easily cause the diaphragm to crack and break. The diaphragm that combines rigidity and flexibility is formed by these flexible dry film materials. When subjected to stress, the dry film can buffer and absorb stress through its own deformation, thereby improving the impact resistance of the device. And when the cavity structure of the device is large, the residual stress of the MEMS process will cause the diaphragm of the device to bulge or dent. This structure composed of flexible dry film materials can play the role of reinforcing ribs. At the same time, since the thermal expansion coefficients of the flexible dry film material and other materials are inconsistent, the stress distribution of the entire diaphragm can be adjusted, so that the diaphragm structure is relatively flat. The piezoelectric composite layer can be divided by at least one gap, forming different piezoelectric composite layer areas around the diaphragm. The gap can reduce the internal stress of the piezoelectric composite film caused by the process.

[0096] As shown in FIG4(k), a schematic diagram of the structure of a MEMS piezoelectric sounder, compared with the piezoelectric MEMS piezoelectric sound unit D19, the piezoelectric MEMS piezoelectric sound unit D21 has three rectangular structural graphics 40c, 40d, and 40e inside the diaphragm, and the three rectangular structures are of the same size, and are regularly distributed inside the diaphragm, presenting a symmetrical structure on the horizontal and vertical axes. The rigid material in the rectangular structural area of ​​the graphics 40c, 40d, and 40e on the diaphragm is removed, and the flexible material 70a covers the three rectangular rigid material removal areas and extends to the upper and lower edges 30b and 30d of the device. Three pieces of flexible material can also be used to cover the three rectangular 40c, 40d, and 40e areas respectively, and the three pieces of flexible material can be unconnected. Of course, it can also be designed that there are multiple rectangular structural graphics inside the diaphragm, and the multiple rectangular structures are of the same size, and are regularly distributed inside the diaphragm, presenting a symmetrical structure on the horizontal and vertical axes. The rigid material of the rectangular structure pattern on the diaphragm is removed, and the multiple rectangular rigid material removal areas are covered with flexible materials. The size of the flexible materials is larger than the rectangular structure and they are not connected to each other. The pattern removed inside the diaphragm of the piezoelectric MEMS piezoelectric sound unit D21 is a rectangular structure, and it can also be composed of one or more patterns such as square, circle, ring, hexagon, polygonal structure, etc. The size and position of the pattern can be various.

[0097] The diaphragm structure of the MEMS piezoelectric sounder can also be formed in other forms, such as the structural schematic diagram of a MEMS piezoelectric sounder as shown in Figure 4(m), the structural schematic diagram of a MEMS piezoelectric sounder as shown in Figure 4(n), the structural schematic diagram of a MEMS piezoelectric sounder as shown in Figure 4(o), the structural schematic diagram of a MEMS piezoelectric sounder as shown in Figure 4(p), the structural schematic diagram of a MEMS piezoelectric sounder as shown in Figure 4(q), and the structural schematic diagram of a MEMS piezoelectric sounder as shown in Figure 4(r). The shape, position, size, etc. of the appropriate slotted structure can be selected according to actual needs, and are not limited here.

[0098] For the above-mentioned piezoelectric MEMS piezoelectric sound unit, if a groove is made on the second piezoelectric composite layer inside the diaphragm structure, when the width of the groove structure is between 0.5μm and 5μm, due to the relatively small size, when the sound propagates in the narrow slit, heat loss and viscous loss will cause the sound wave to attenuate, and flexible material may not be used for covering; see FIG. The groove structure of device D18 is greater than 5um, and is covered with flexible material to prevent sound leakage. The width of the flexible material of device D20 is greater than the groove structure, and the flexible material may be used to cover all or part of the gap, and the entire or part of the diaphragm may be covered at the same time.

[0099] The MEMS piezoelectric sounder is a sound-generating device that produces sound by deflecting the diaphragm structure. When the applied drive signal frequency is significantly lower than the resonant frequency of the device, the deflection of the diaphragm structure can be directly controlled by the applied drive voltage signal. The deflection of the diaphragm structure is also related to the transverse piezoelectric coefficient of the piezoelectric film. When the diaphragm structure operates within the linear range, the drive signal is much lower than the resonant frequency during the period, and the deflection of the diaphragm structure is proportional to the applied voltage and the transverse piezoelectric coefficient of the piezoelectric film.

[0100] The mechanical resonance point of the MEMS piezoelectric sounder in this embodiment can be designed to be within the audio range, or beyond its range of 20KHz, or even in the ultrasonic frequency band, through the thickness of the membrane layer and the size of the cavity. When the mechanical resonance point is designed to be within the audible sound range of 20Hz-20kHz and the first-order resonance frequency is 4-10KHz, the diaphragm drive displacement is large under the drive of the piezoelectric signal, and the output sound pressure level of the MEMS piezoelectric sounder in the low-frequency range is large, and it can be used in low-frequency speakers. When the mechanical resonance point of the MEMS piezoelectric sounder is designed to be greater than 20kHz outside the audible sound, the first and third odd harmonics of the MEMS piezoelectric sounder are outside the audible sound frequency range, and the MEMS piezoelectric sounder has low nonlinearity and low THD, and can be used in high-frequency speakers.

[0101] The above-mentioned MEMS piezoelectric sounder maintains the symmetry of the structure and ensures the consistency of the vibration mode. When driven, the rectangular structure only has odd-order vibration modes such as the first, third, and fifth orders, and there are no even-order vibration modes that cancel each other out. This can broaden the bandwidth of the MEMS device, eliminate the harmonic interference caused by even-order vibrations, and reduce THD.

[0102] Taking the cross-sectional view of the MEMS piezoelectric sounder D19 in FIG. 4(i) as an example, a polarization mode and electrical connection schematic diagram of a MEMS piezoelectric sounder as shown in FIG. 5(a), a polarization mode and electrical connection schematic diagram of a MEMS piezoelectric sounder as shown in FIG. 5(b), a polarization mode and electrical connection schematic diagram of a MEMS piezoelectric sounder as shown in FIG. 5(c), and a polarization mode and electrical connection schematic diagram of a MEMS piezoelectric sounder as shown in FIG. 5(d) are provided. The first piezoelectric composite layer 10a and 10c exist on the left and right sides of the MEMS piezoelectric sounder D19, and there is no second piezoelectric composite layer in the center of the diaphragm structure. As shown in FIG. 5(a), FIG. 5(b), FIG. 5(c), and FIG. 5(d), the direction of the piezoelectric layer indication arrow in the piezoelectric composite layer 10a and 10c (upward or downward along the Z-axis direction) is the polarization direction of the device piezoelectric layer, and the positive and negative symbols in the top electrode layer, the middle electrode layer, and the bottom electrode layer in the piezoelectric composite layer 10a and 10c represent the positive and negative electrodes. As shown in FIG5(a), the polarization directions of all the upper and lower piezoelectric layers of the MEMS piezoelectric sounder are consistent and upward. In terms of electrical connection, the middle electrode layers of the piezoelectric composite layers 10a and 10c are connected to the negative, and the top electrode layer and the bottom electrode layer are connected to the positive in parallel. The piezoelectric composite layers 10a and 10c are electrically connected in that the negative electrode is connected to the negative electrode, and the positive electrode is connected to the positive electrode. The connection mode of the two piezoelectric composite layers 10a and 10c is a parallel structure.

[0103] Figure 5(b) , 5(c) , 5(d), the polarization directions of the piezoelectric layers in the piezoelectric composite layers 10a and 10c are different. For example, in FIG5(b), the polarization directions of the upper and lower piezoelectric layers in the piezoelectric composite layers 10a and 10c are both downward, in FIG5(c), the polarization direction of the bottom piezoelectric layer in the piezoelectric composite layers 10a and 10c is upward, and the polarization direction of the upper piezoelectric layer is downward, and in FIG5(d), the polarization direction of the bottom piezoelectric layer in the piezoelectric composite layers 10a and 10c is downward, and the polarization direction of the upper piezoelectric layer is upward. In FIG5(b), FIG5(c), and FIG5(d), the electrical connection is as follows: the middle layer electrodes of the piezoelectric composite layers 10a and 10c are connected to the negative electrode, the top electrode layer and the bottom electrode layer are connected to the positive electrode in parallel, and the electrical connection between the piezoelectric composite layers 10a and 10c is that the negative electrode is connected to the negative electrode, and the positive electrode is connected to the positive electrode, and the connection mode of the two piezoelectric composite layers 10a and 10c is a parallel structure. The four electrical connection modes shown in Figure 5(a), Figure 5(b), Figure 5(c), and Figure 5(d) are two-terminal interfaces, with only positive and negative interfaces, or signal ports and ground ports. The effects of the four different polarization modes shown in Figure 5(a), Figure 5(b), Figure 5(c), and Figure 5(d) on device performance can be compared through simulation.

[0104] Provided below are schematic diagrams of simulation results of a MEMS piezoelectric sounder as shown in FIG6(a), a schematic diagram of simulation results of a MEMS piezoelectric sounder as shown in FIG6(b), a schematic diagram of simulation results of a MEMS piezoelectric sounder as shown in FIG6(c), and a schematic diagram of simulation results of a MEMS piezoelectric sounder as shown in FIG6(d), which correspond to four displacement diagrams of the diaphragm structure of the MEMS piezoelectric sounder under four different polarization modes, respectively, and the maximum displacements obtained by simulation are: -11.3um, 11.3um, 28.8um, -28.8um, and comparing the displacement performance of the devices, it can be seen that when the middle electrode layer is grounded, the top electrode layer and the bottom electrode layer are connected in parallel, and the polarization directions of the upper and lower piezoelectric layers of the piezoelectric composite layer are opposite, that is, the maximum displacement can be obtained in the cases of FIG5(c) and FIG5(d).

[0105] In FIG. 5(a) and FIG. 5(b), the arrows indicating the upper and lower piezoelectric layers in the piezoelectric composite layers 10a and 10c are all upward or all downward along the Z-axis direction. In order to make the performance of the MEMS piezoelectric sounder have a good displacement as shown in FIG. 5(c) and FIG. 5(d), the electrical connection mode of the piezoelectric composite layers 10a and 10c can be changed, as shown in FIG. 7(a) and FIG. 7(b), respectively. The middle electrode layer of each piezoelectric composite layer 10a and 10c is grounded, and the top electrode layer and the bottom electrode layer are connected to positive and negative, respectively, or the top electrode layer and the bottom electrode layer are connected to negative and positive, respectively. Then, the piezoelectric composite layers 10a and 10c are electrically connected to the ground, the negative electrode is connected to the negative electrode, and the positive electrode is connected to the positive electrode. The connection mode between the two piezoelectric composite layers 10a and 10c is a parallel structure. The simulation results show that the absolute value of the maximum displacement of the diaphragm structure in Figure 7(a) and Figure 7(b) is equal to 28.8μm, and the maximum displacement directions of Figure 7(a) and Figure 7(b) are opposite. The electrical connection method of Figure 7(a) and Figure 7(b) is a three-terminal interface, and the positive, negative and ground interfaces are differential. Compared with the two electrical connection methods of Figure 5(c) and Figure 5(d), the device performance is consistent.

[0106] Below Figure 2Taking the MEMS piezoelectric sounder D10 in the figure as an example, a polarization mode and electrical connection schematic diagram of a MEMS piezoelectric sounder as shown in FIG8(a), a polarization mode and electrical connection schematic diagram of a MEMS piezoelectric sounder as shown in FIG8(b), a polarization mode and electrical connection schematic diagram of a MEMS piezoelectric sounder as shown in FIG8(c), and a polarization mode and electrical connection schematic diagram of a MEMS piezoelectric sounder as shown in FIG8(d) are provided. In FIG8(a), FIG8(b), FIG8(c), and FIG8(d), the direction of the arrow indicates the polarization direction of the piezoelectric layer of the device. The polarization directions of all piezoelectric layers in the piezoelectric composite layers 10a, 10b, and 10c in FIG8(a) and FIG8(b) are consistent, and are all upward or all downward along the Z-axis direction. The positive and negative symbols in the top electrode layer, the middle electrode layer, and the bottom electrode layer of the piezoelectric composite layers 10a, 10b, and 10c represent positive and negative electrodes. As shown in FIG8(a), the device is electrically connected with the piezoelectric composite layers 10a and 10c having their respective middle layer electrodes grounded, and the upper and lower electrode layers connected in parallel to positive, and the piezoelectric composite layer 10b having its middle layer electrodes grounded, and the upper and lower electrode layers connected in parallel to positive. The piezoelectric composite layers 10a and 10c in FIG8(a) and FIG8(b) are electrically connected with the ground being grounded, the positive electrode being connected to the positive electrode, and the connection mode of the two piezoelectric composite layers 10a and 10c is a parallel structure. In FIG8(a), the electrical connection between 10a, 10c and 10b is grounded, the positive electrode is connected to the positive electrode, and the connection mode between 10a, 10b and 10c is a parallel structure; in FIG8(b), the polarity of the upper and lower electrodes of the piezoelectric composite layer 10b can be opposite, with the upper electrode layer connected to the negative and the lower electrode layer connected to the positive. The electrical connection between 10a, 10c and 10b is grounded, the positive electrode is connected to the positive electrode, and the connection mode between 10a, 10b and 10c is a series structure.

[0107] The polarization directions of all upper and lower piezoelectric layers in the piezoelectric composite layers 10a and 10c in FIG8(c) and FIG8(d) are opposite, and the polarization directions of all upper and lower piezoelectric layers in 10b are the same. For example, in FIG8(c), the polarization direction of the bottom piezoelectric layer of 10a and 10c is upward along the Z-axis direction, and the polarization direction of the top piezoelectric layer is downward along the Z-axis direction. The upper and lower piezoelectric layers of the piezoelectric composite layers 10a, 10b, and 10c can be reversed, that is, the polarization direction of the top piezoelectric layer is upward along the Z-axis direction and the polarization direction of the bottom piezoelectric layer is downward along the Z-axis direction. In FIG8(c) and FIG8(d), the middle layer electrodes of the piezoelectric composite layers 10a, 10b, and 10c are grounded in electrical connection, and the upper and lower electrode layers of 10a and 10c are connected in parallel to the positive. In Figure 8(c) and Figure 8(d), the electrical connection between 10a and 10c is grounded, the positive electrode is connected to the positive electrode, and the connection between the two piezoelectric composite layers 10a and 10c is a parallel structure. In Figure 8(c) and Figure 8(d), the electrical connection between 10a, 10c and 10b is: grounded, the positive electrode is connected to the positive electrode, and the connection between 10a, 10b and 10c is a parallel structure. In Figure 8(c), the polarities of the upper and lower electrodes of the piezoelectric composite layer 10b can be opposite and both negative; in Figure 8(d), the polarities of the upper and lower electrodes of the piezoelectric composite layer 10b can be opposite and both negative. Through simulation, it can be known that under the polarization direction and electrode connection of Figure 8(d), the diaphragm structure will obtain the optimal offset.

[0108] As shown in FIG9(a), a schematic diagram of polarization mode and electrical connection of a MEMS piezoelectric sounder, and as shown in FIG9(b), a schematic diagram of polarization mode and electrical connection of a MEMS piezoelectric sounder, the arrows indicating the upper and lower piezoelectric layers in the piezoelectric composite layers 10a, 10b, and 10c are all upward or all downward along the Z-axis direction. In FIG9(a), the arrows indicating the upper and lower piezoelectric layers in the piezoelectric composite layers 10a and 10c are upward along the Z-axis direction, 10b is upward, or the arrows of 10a, 10b, and 10c are all opposite, and the direction of the arrow indicates the polarization direction of the piezoelectric layer of the device. In order to achieve the optimal maximum displacement of the device performance, the electrical connection mode of the device D10 is shown in FIG9(a) and FIG9(b). In FIG9(a), the polarization direction of each voltage layer is upward or downward, and in terms of electrical connection, the middle layer electrodes of the piezoelectric composite layers 10a and 10c are grounded, the upper and lower electrode layers are connected to positive and negative, or the upper and lower electrode layers are connected to negative and positive, and the piezoelectric composite layer 10b is just opposite to 10a and 10c. Then the piezoelectric composite layers 10a and 10c are electrically connected to the ground, the negative electrode is connected to the negative electrode, and the positive electrode is connected to the positive electrode. The connection between the two piezoelectric composite layers 10a and 10c is a parallel structure, and the connection between the piezoelectric composite layers 10a and 10c and the unit 10b is grounded, the negative electrode is connected to the positive electrode, and the positive electrode is connected to the negative electrode. The connection between them is a series structure; in Figure 9 (b), the upper and lower piezoelectric layer indication arrows in the piezoelectric composite layers 10a and 10c are downward along the Z axis, 10b is upward, or the arrows of 10a, 10b, and 10c are all opposite. Then the piezoelectric composite layers 10a, 10b, and 10c are electrically connected to the ground, the negative electrode is connected to the negative electrode, and the positive electrode is connected to the positive electrode. The connection between the three piezoelectric composite layers 10a, 10b, and 10c is a parallel structure. When the arrows of the piezoelectric composite layers 10a, 10b, and 10c point to opposite directions and the polarization directions are changed, the connection between the three piezoelectric composite layers 10a, 10b, and 10c is still a parallel structure, but the displacements are equal in magnitude and opposite in direction.

[0109] The positive and negative symbols in the top electrode layer, the middle electrode layer and the bottom electrode layer of the above-mentioned piezoelectric composite layer represent positive and negative electrodes. When the polarity of the top electrode layer and the bottom electrode layer of the same piezoelectric composite layer is the same, the upper and lower electrodes are connected in parallel to the electrical signal end, and the middle electrode layer is grounded. Of course, the top electrode layer and the bottom electrode layer can also be connected in parallel to the ground, and the middle electrode layer is connected to the signal end. At the same time, when there are two or more piezoelectric layers in the piezoelectric composite layer, and there are two or more piezoelectric composite layers on the diaphragm structure, the performance of the device is related to the polarization direction of the piezoelectric layer of the piezoelectric composite layer in each region and the electrical connection between the electrode layers of each unit. Only when the polarization direction of the piezoelectric layer and the electrical connection method are appropriate, the acoustic performance output sound pressure level SPL of the device will be optimal.

[0110] An embodiment of the utility model provides a speaker, comprising at least one MEMS piezoelectric sound generator according to any one of the above items, and each MEMS piezoelectric sound generator is arranged in a preset array form.

[0111] In order to produce sound, 1) the larger the effective radiation area, the higher the sound pressure generated. 2) the greater the displacement of the diaphragm radiation area, the higher the sound pressure generated. When a speaker device of a single MEMS piezoelectric sounder has a limited output sound pressure level SPL under excitation, multiple MEMS piezoelectric sounders can be distributed in an array structure to increase the area of ​​the speaker to generate sound, thereby improving the sound pressure level output of the device. An array arrangement schematic diagram is shown in Figure 10(a), an array arrangement schematic diagram is shown in Figure 10(b), and an array arrangement schematic diagram is shown in Figure 10(c).

[0112] Figure 10(a) uses the same structure of MEMS piezoelectric sounders, and the unit device size parameters, structural shape, and performance in the array are consistent. The array structure layout is a linear structure, with a horizontal axis and a vertical axis arranged linearly. This figure takes the MEMS piezoelectric sounder D10 as an example. It can be arranged in the horizontal axis X direction as two units of device D10-D10, or three units of device D10-D10-D10, etc., as well as a variety of other unit arrangements; it can be arranged in the vertical axis Y direction as a device D10, or four units of device D10-D10-D10-D10, etc., as well as a variety of other unit arrangements; at the same time, it can be arranged linearly in the horizontal and vertical axes, using device D10 to arrange in 1x 1, 2x2, 3x3, 2x3, 3x2, 4x4 and other array structures. The MEMS piezoelectric sounder D10 may be used in the array structure, and other MEMS piezoelectric sounders, such as the MEMS piezoelectric sounder D11, the MEMS piezoelectric sounder D12, etc., may also be used to form an array structure of multiple identical devices.

[0113] The array structure layout in Figure 10(b) has a linear arrangement of the horizontal and vertical axes. In the horizontal axis X direction, the MEMS piezoelectric sound generator D11 is arranged in a single or multiple identical units, and the devices in the horizontal axis X direction are the same; in the vertical axis Y direction, the MEMS piezoelectric sound generator D12 is arranged in a single or multiple identical units, and the devices in the vertical axis Y direction are different; the horizontal and vertical axes can be arranged linearly at the same time, and the MEMS piezoelectric sound generators D11 and MEMS piezoelectric sound generators D12 can be arranged in a variety of different array structures such as 2x2, 3x3, 4x4, 2x3, 3x2, etc. Other MEMS piezoelectric sound generators can also be used in the array structure, such as MEMS piezoelectric sound generator D14 and / or MEMS piezoelectric sound generator D15.

[0114] The array structure layout in Figure 10(c) has a linear arrangement of the horizontal and vertical axes. In the horizontal axis X direction, the MEMS piezoelectric sound generator D14 is arranged as a single or multiple units, and the MEMS piezoelectric sound generators in the horizontal axis X direction are different; in the vertical axis Y direction, the MEMS piezoelectric sound generator D13 is arranged as a single or multiple units, and the MEMS piezoelectric sound generators in the vertical axis Y direction are different; it can be arranged linearly in both the horizontal and vertical axes, using MEMS piezoelectric sound generators D14 and MEMS piezoelectric sound generators D16, MEMS piezoelectric sound generators D13 and MEMS piezoelectric sound generators D15 in the horizontal axis X direction, arranged in a variety of different array structures such as 2x2, 3x3, 4x4, 2x3, 3x2, etc. It should be noted that the MEMS piezoelectric sound generators in the array can be other MEMS piezoelectric sound generators, such as MEMS piezoelectric sound generators D17 and / or MEMS piezoelectric sound generators D20, etc.

[0115] Of course, other array arrangements may also be selected according to actual needs, such as an array arrangement schematic diagram shown in FIG. 11(a), an array arrangement schematic diagram shown in FIG. 11(b), an array arrangement schematic diagram shown in FIG. 11(c), an array arrangement schematic diagram shown in FIG. 12(a), and an array arrangement schematic diagram shown in FIG. 12(b). Figure 13(a) , 13(b) , 13(c), 13(d), 13(e), 13(f), 13(g), and 13(h) are schematic diagrams of array arrangements. Appropriate arrangements may be selected based on actual needs and are not limited here.

[0116] In this embodiment, when used as a loudspeaker, depending on the size of the emitted sound pressure level, the loudspeaker can be a single MEMS piezoelectric sound generator, or it can be a plurality of MEMS piezoelectric sound generators arranged in a preset array and driven by electrical parallel connection to increase the output sound pressure level, wherein the diaphragm structures of the plurality of MEMS piezoelectric sound generators are coplanar.

[0117] When used as a speaker, there are a variety of electrical connection methods according to the number of piezoelectric layers and the polarization directions of the piezoelectric layers in different regions. By comparison, the optimal connection method that maximizes the device diaphragm displacement and outputs the highest sound pressure level can be obtained.

[0118] If the polarization directions of the piezoelectric layers in all the MEMS piezoelectric sounders on the upper side of the diaphragm structure are the same, the electric fields of the piezoelectric layers in the inner and outer composite layers on the spring structure are opposite, the inner and outer electrodes are electrically divided, and the electrode layers are connected in series; if the polarization directions of the piezoelectric layers in all the MEMS piezoelectric sounders on the upper side of the diaphragm structure are opposite, the electric fields of the piezoelectric layers in the inner and outer composite layers on the spring structure are the same, the inner and outer electrodes are electrically divided, and the electrode layers are connected in parallel.

[0119] The MEMS piezoelectric sounder and speaker of the embodiment of the utility model can be used as a MEMS actuator, specifically a piezoelectric MEMS driver, a piezoelectric MEMS micropump, a piezoelectric MEMS micromirror, a piezoelectric MEMS switch, a piezoelectric MEMS inkjet print head, etc. Conversely, it can also be used as a MEMS transducer and sensor, specifically a piezoelectric MEMS microphone, a piezoelectric MEMS pressure gauge, a piezoelectric MEMS ultrasonic transducer, a piezoelectric MEMS accelerometer, etc.

[0120] The structure of the above-mentioned loudspeaker is verified below. FIG14(a) is a schematic diagram of a loudspeaker, which is a MEMS loudspeaker device A having an array structure composed of four square units. FIG15(a) is a schematic diagram of a loudspeaker, which is a MEMS loudspeaker device B having an array structure composed of three rectangular units. MEMS loudspeaker devices A and B having the same size (length, width and thickness of each membrane layer) are manufactured under the same process conditions. Single units of devices A and B are simulated when driven by a 15V voltage to obtain the resonant frequency of the corresponding structure and the maximum vibration displacement of the diaphragm. The simulation results shown in Figures 14(b) and 14(c) are the simulation results of the resonant frequency and diaphragm displacement of device A; the simulation results shown in Figures 15(b) and 15(c) are the simulation results of the resonant frequency and diaphragm displacement of device B. It can be seen from the figure that the resonant frequencies of the unit structures of MEMS speakers A and MEMS speakers B are 9.79kHz and 11.8kHz respectively, and the maximum displacements are 48.2um and 49.8um respectively. By integrating the displacement of the device diaphragm, the volume of air pushed by the corresponding MEMS speakers A and MEMS speakers B is 0.435mm^3 and 0.519mm^3. Comparing MEMS speakers A and MEMS speakers B, the resonant frequency of the unit simulation of MEMS speakers B is larger than that of MEMS speakers A, and the maximum displacement of the device diaphragm under voltage driving is also larger. This is because the rectangular structure is better than the square structure and the amount of air pushed is also larger, that is, the emission sound pressure level of the acoustic transducer is higher.

[0121] The above-mentioned MEMS piezoelectric sounder has a gap for mechanical decoupling. When the width of the gap is 0.5 to 5um, it can not only reduce the internal stress of each film layer in the device's vibrating film caused by the process, but also use flexible materials for covering to improve the flexibility of the diaphragm, reduce the sound leakage of the device at low frequencies, and increase the vibration amplitude and emission sound pressure level of the piezoelectric MEMS generator. For devices with cantilever beam structures, flexible materials can be used to make springs connected to form an integral structure, so that the diaphragm will maintain consistency in posture when vibrating. When the width of the slotted structure is 5μm to 200μm, the silicon diaphragm with a higher density is removed and replaced with a flexible material with a lower density, which reduces the mass of the diaphragm and is conducive to improving the sound pressure level curve and improving the mid-frequency performance.

[0122] The above-mentioned MEMS piezoelectric sounder is a rectangular structure. Compared with the circular and square structures, the sound unit response spectrum lacks even modes. Multiple modes are excited in a narrow frequency range. The excited modes are all odd modes. Multiple modes are merged together, so the frequency bandwidth is significantly widened. And under the same size area, the rectangular array structure has higher performance and can improve the sound pressure level SPL of the sound device.

[0123] The solution is based on a double-layer piezoelectric PZT film, and through reasonable polarization of the piezoelectric layer and electrical connection of different regions, the dual drive electrodes (inner and outer electrodes) use a piston mode with a 180° anti-phase drive structure to improve the emission sound pressure level of the MEMS piezoelectric sounder and speaker.

[0124] This embodiment adopts a diaphragm structure that combines rigidity and flexibility, and uses flexible materials to cover the slotted structure to reduce low-frequency sound leakage and improve the sound pressure level output at low frequencies. At the same time, the damping of the diaphragm system is also increased, and the quality factor Q value is reduced, thereby reducing or reducing resonance within a larger sound frequency range. The nonlinearity caused by the large diaphragm excursion of the device resonant frequency is reduced, thereby reducing the total harmonic distortion THD and intermodulation distortion IM. At the same time, a double-layer piezoelectric thin film structure device with a rectangular cantilever beam or a bridge structure fixed at both ends is designed, and an array structure composed of multiple units is used to improve the output sound pressure level of the MEMS piezoelectric sound unit and the speaker.

[0125] In the utility model, the MEMS piezoelectric sounder and speaker perform electroacoustic conversion through a piezoelectric composite layer, and an electrical signal is applied to the piezoelectric composite layer, and the piezoelectric layer is deformed to drive the diaphragm to vibrate, thereby emitting sound. In some embodiments, the sound-generating device may be a miniature speaker, an ultrasonic transducer, or other suitable device to convert the electrical signal into sound waves. At the same size area and resonant frequency, the rectangular structure pushes out more air than the square, circular, hexagonal and other structures, and is therefore more effective. The modes excited by the cantilever beam or bridge-type rectangular structure are all odd modes. When the aspect ratio of the device is larger, the spacing between adjacent resonant frequencies will be smaller, increasing the damping of the system, reducing the quality factor of the device resonance, and merging the related peaks of the excited different modes together to form an ultra-wide frequency bandwidth.

[0126] The present utility model also provides a method for preparing a MEMS piezoelectric sound generator, such as Fig.16 As shown, the method comprises the following steps:

[0127] Step S1601, thermally grow an insulating layer on the upper surface and the lower surface of a preset substrate respectively;

[0128] The above-mentioned preset substrate can be a SOI substrate, a silicon substrate, glass, sapphire, etc.; taking the preset substrate as an SOI substrate as an example, the SOI substrate usually has an insulating buried layer, which can also be called a BOX layer. The BOX layer can divide the substrate into two parts. The upper part of the BOX layer can correspond to the aforementioned SOI top silicon, and the lower part of the BOX layer can correspond to the aforementioned SOI base silicon. The parasitic junction capacitance can be reduced by the BOX layer; the insulating layer can be thermally grown on the upper and lower surfaces of the SOI substrate, respectively. The thickness of the insulating layer is between 0.1 and 15 um, and can be made of insulating materials such as silicon nitride and aluminum oxide. Fig.17 The cross-sectional schematic diagram of a substrate with an insulating layer grown thereon is shown, wherein the upper and lower black areas in the figure are the insulating layers.

[0129] Step S1602, depositing a seed layer, a bottom electrode layer, an intermediate layer and a top electrode layer in sequence from bottom to top on the insulating layer on the upper surface of the substrate to obtain a first element; wherein the intermediate layer is a piezoelectric layer, or the intermediate layer is formed by overlapping and stacking a plurality of piezoelectric layers and a plurality of electrode layers; wherein a layer above the bottom electrode layer and a layer below the top electrode layer are both piezoelectric layers;

[0130] A bottom electrode layer, a bottom piezoelectric layer, a middle electrode layer, a top piezoelectric layer and a top electrode layer are grown. For example, the two piezoelectric layers of the piezoelectric MEMS generating unit D10 are single crystal PZT thin films. In this case, the thickness of the PZT is 1.5 um each.

[0131] The material of the piezoelectric layer may be selected from but is not limited to one of the following materials or a combination thereof: polycrystalline or single crystal piezoelectric films such as ZnO, AlN, PZT, PVDF, or doped piezoelectric films, such as AlN doped piezoelectric films; the thickness of the piezoelectric layer is between 0.1μm and 25μm, and the thickness of the two layers of piezoelectric films can be the same or different.

[0132] The seed layer is conducive to the high-quality growth of the piezoelectric layer; the materials of the bottom electrode layer, the middle electrode layer, and the top electrode layer may be selected from but not limited to one of the following materials or a combination thereof: single crystal or polycrystalline metal films such as aluminum, copper, gold, platinum, molybdenum, chromium, titanium, etc., metal conductive films such as nickel oxide (LNO), SRO, or composite metal layers, such as: gold / chromium composite layers. Preferably, the thickness of the Pt electrode is between 0.01μm and 5μm, and the thickness of each electrode layer film can be the same or different. In this case, the thickness of Pt is 0.15μm, etc.

[0133] like Fig.18 A cross-sectional schematic diagram after the bottom electrode layer is grown is shown in FIG. Fig.19 A cross-sectional schematic diagram after the growth of the intermediate layer and the top electrode layer is shown. Fig.19 The middle layer in the figure is illustrated by taking two piezoelectric layers as an example.

[0134] Step S1603, patterning the top electrode layer, the middle layer and the bottom electrode layer in the first element in sequence to form a symmetrical first piezoelectric composite layer at a set of designated edge positions opposite to each other on the upper surface of the substrate, thereby obtaining a patterned second element;

[0135] Using key processes such as wet etching and dry etching, the PZT piezoelectric film is etched at an angle, which is beneficial to the step coverage of the passivation layer. The etching angle of the PZT piezoelectric film is 30°-60°, and the over-etching amount of the middle electrode and the bottom electrode is <30%. The roughness of the PZT side wall: the smaller the better. The goal is to have no delamination between the sliced ​​PZT and the passivation layer after the passivation layer is deposited.

[0136] The electrode layer and the piezoelectric layer in the first element are patterned, and after the top electrode layer, the top piezoelectric layer, the middle electrode layer, the bottom piezoelectric layer and the bottom electrode layer are patterned, the Overlay size between the layers is less than 3um. Fig. 20 A graphical cross-sectional schematic diagram is shown, which is a schematic diagram of Fig.19 A cross-sectional view obtained after the top electrode layer, top piezoelectric layer, middle electrode layer, bottom piezoelectric layer and bottom electrode layer are sequentially patterned.

[0137] The redundant piezoelectric layer and electrode layer in the vibration area are completely removed to maintain the symmetry of the structure and ensure the consistency of the vibration mode. When driven, the rectangular structure only has odd-order vibration modes such as the first, third, and fifth orders, and no even-order vibration modes that cancel each other out.

[0138] Step S1604, depositing a passivation layer on the second element to isolate the electrical connection of each top electrode layer, and patterning the passivation layer to form a pad area to lead out the bottom electrode layer, the middle electrode layer, and the top electrode layer of each first piezoelectric composite layer to obtain a third element;

[0139] The passivation layer can isolate the electrical connections of each electrode layer, play an insulating and protective role, and the patterned passivation layer leads to the bottom electrode layer, the middle electrode layer and the top electrode layer, which are used for the electrical connection between different piezoelectric composite layers and the connection pad PAD. In the embodiment, the passivation layer needs to have good step coverage and can fit tightly on each film layer. The material can be selected from but is not limited to one of the following materials or a combination thereof: silicon dioxide, aluminum nitride, PI, aluminum oxide and other oxide insulating materials, or non-conductive organic compounds, etc., with a thickness in the range of 0.05μm to 5μm. Fig.21 A schematic cross-sectional view of a passivation layer after deposition and patterning is shown.

[0140] Step S1605, depositing a metal layer on each pad region in the third component to form a pad, thereby obtaining a fourth component;

[0141] like Fig. 22 A schematic cross-sectional view of a metal wire after deposition and patterning is shown. In an embodiment, a lift-off process can be used to deposit and pattern the metal wire, lead the top and bottom electrode layers to the welding pad PAD, and connect the piezoelectric composite layers in various regions, such as parallel connection between units, series connection between units, etc. The material can be selected from but not limited to one of the following materials or a combination thereof: gold, copper, aluminum, and other metal materials, or conductive alloy materials, etc., and the thickness can be in the range of 0.1 to 3μm.

[0142] Step S1606, etching a designated area on the upper surface of the fourth element to form a plurality of slotted structures, and covering at least a portion of the slotted structures with a flexible material to obtain a fifth element;

[0143] like Fig.23 The cross-sectional diagram of a SOI top silicon groove after etching is shown. In the embodiment, the SOI top silicon etching adopts the DRIE process, which has a good depth-to-width ratio and can etch the specified area of ​​the Si layer of the upper surface substrate device of the fourth element. The shape of the groove obtained by etching is: inner and outer rings, and long grooves, but it can also be an etched area layer of other shapes, including squares, rectangles or polygons, etc. The etching thickness can be between 0.5μm-35μm, and the width of the ring in the circular or square ring groove is between 5μm-2000μm, etc. Fig.24 The schematic cross-sectional view of a structure coated with a flexible material is shown, with the slotted gaps being covered with a flexible film material.

[0144] Step S1607, thinning and etching a cavity on the bottom surface of the substrate of the fifth element to obtain a MEMS piezoelectric sounder; wherein the cavity obtained by etching is located in the bottom center area of ​​the substrate.

[0145] In this embodiment, the wafer can be thinned, and the back cavity Si layer and the BOX layer can be etched by DRIE. Specifically, the back cavity can be etched by DRIE, and the BOX layer of SOI can be etched. Wafer thinning CMP (Chemical-MechanicalPlanarization) to 300 μm is conducive to the thinning of the device thickness. The back cavity and the BOX layer of SOI are etched by DRIE using double-sided exposure technology, so as to obtain a piezoelectric MEMS generating unit with a cavity and a diaphragm structure, such as Figure 1 shown.

[0146] The DRIE etching back cavity etching accuracy of the device has a great impact on the device performance, especially the change in the width of the cavity. When the cavity etching width is larger than the original design, the resonant frequency of the device will be reduced. When the cavity etching width is too large, it may even cause the diaphragm to rupture. Therefore, the accuracy of the alignment mark, whether the device etching is accurate, whether the etching is complete, and whether there is over-etching require strict control of the process. The back cavity etching angle is required to be: 90°±1.5°, without residue and over-etching.

[0147] The preparation method of the above-mentioned MEMS piezoelectric sounder includes: providing an SOI wafer, which includes: a base silicon layer, a Box layer-silicon dioxide, and a device silicon layer. By depositing a piezoelectric composite layer on the wafer, and patterning the piezoelectric composite layer through an etching process, piezoelectric composite layers in different regions are formed; a passivation layer is deposited to electrically isolate and protect the piezoelectric composite layer in each region, and an electrode connection area of ​​the piezoelectric composite layer is reserved for electrical connection of metal wires; the device silicon layer is etched through an etching process, and the diaphragm is etched to form a slotted structure. The flexible dry film material is laminated by vacuum lamination, and the flexible film is patterned by the MEMS process, and the flexible film covers the slotted structure; the back of the device is DRIE-etched to form a cavity structure of the sounder, and the process stops at the Box layer, and the Box layer is wet-etched to release the cavity diaphragm structure.

[0148] The preparation method of the above-mentioned MEMS piezoelectric sounder can reduce the internal stress of each membrane layer in the diaphragm structure caused by the process by setting a slotted structure; the use of flexible materials to cover the slotted structure can improve the flexibility of the diaphragm structure, while reducing the sound leakage of the MEMS piezoelectric sounder at low frequencies, and improving the sound pressure level output at low frequencies. Designing a double-layer piezoelectric film rectangular bridge unit structure with reinforced ends and multiple units to form an array can push out more air volume, improve the vibration amplitude and emission sound pressure level of the MEMS piezoelectric sounder, and replace the silicon diaphragm with a high density with a low-density flexible material to reduce the mass of the diaphragm structure. The rigid-flexible diaphragm structure increases the damping of the diaphragm system and reduces the vibration quality factor Q value, thereby reducing or reducing resonance within a larger sound frequency range. Reduce the nonlinearity caused by the large diaphragm excursion at the resonant frequency of the device, thereby reducing the total harmonic distortion THD and intermodulation distortion IM, which is conducive to improving the sound pressure level SPL frequency response curve and THD frequency response curve, thereby improving the sound quality of the MEMS piezoelectric sounder.

[0149] This embodiment mainly improves the following contents: (1) The structural form of MEMS piezoelectric sounders, such as cantilever beams, cantilever beams with spring connections or bridge structures, distribution of piezoelectric composite layers, different shapes, sizes and positions of open gaps, and rectangular device structures covered with flexible materials, and different shapes, sizes and positions covered by flexible materials. (2) The process manufacturing method based on flexible dry film MEMS piezoelectric devices. (3) The polarization method based on double-layer piezoelectric PZT film and the electrical connection method of different piezoelectric composite layers. 4) The structural form of MEMS piezoelectric speaker arrays, in which sound units with different resonant frequencies can be set in the array structure, so that multiple relatively wide-band smooth peaks are mixed together to form a frequency response that is relatively flat to the resonant frequency.

[0150] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the utility model.

Claims

1. A MEMS piezoelectric sounder, characterized in that: include: A substrate, wherein a first piezoelectric composite layer is symmetrically arranged at a set of designated edge positions opposite to each other on an upper surface of the substrate; Each of the first piezoelectric composite layers is a rectangular structure; The bottom center area of ​​the substrate has a cavity, and at least a portion of each of the first piezoelectric composite layers is located in an upper area of ​​the substrate corresponding to the cavity; In the upper area, a plurality of slotted structures are arranged in a designated area except for at least a part of each of the first piezoelectric composite layers, at least a part of the slotted structures are covered with a flexible material, and the upper area with the flexible material forms a diaphragm structure of the MEMS piezoelectric sounder; the diaphragm structure is a rectangular bridge structure; the first diaphragm edge of the diaphragm structure is an anchoring edge, and the other diaphragm edges except the first diaphragm edge are non-anchoring edges; an edge slotted structure is respectively arranged on each of the non-anchoring edges, and the first diaphragm edge is determined according to the relative position of the first piezoelectric composite layer on the substrate.

2. The MEMS piezoelectric sounder according to claim 1, characterized in that: The edge slot structures corresponding to the two opposite non-anchoring edges are parallel to each other, and the sizes of the edge slot structures are the same.

3. The MEMS piezoelectric sounder according to claim 1, characterized in that: The diaphragm structure is parallel to the upper surface of the substrate, and at least a portion of the anchoring edge is fixed on the substrate.

4. The MEMS piezoelectric sounder according to claim 1, characterized in that: At least one second piezoelectric composite layer is provided in the upper region of the substrate; a groove structure is provided on each of the second piezoelectric composite layers, and / or a groove structure is provided in a region other than each of the second piezoelectric composite layers in the designated region; and the groove structure is covered with a flexible material.

5. The MEMS piezoelectric sounder according to claim 1, characterized in that: The aspect ratio of the diaphragm structure is greater than a preset value; As the aspect ratio of the diaphragm structure increases, the value of the first-order resonance frequency of the MEMS piezoelectric sound generator increases, and the difference between the resonance frequencies of each order decreases.

6. The MEMS piezoelectric sounder according to claim 5, characterized in that: The thickness range of the diaphragm structure is 0.1 μm to 50 μm; as the thickness of the diaphragm structure is thinner, the value of the first-order resonance frequency is smaller, and under the same piezoelectric drive, the deflection displacement generated by the diaphragm structure is larger, and the amount of air pushed out is greater.

7. The MEMS piezoelectric sounder according to claim 5, characterized in that: The larger the size of the cavity, the smaller the value of the first-order resonant frequency; wherein the size includes at least one of the following: the cavity area, cavity length, cavity width, cavity radius, and cavity diameter.

8. The MEMS piezoelectric sounder according to claim 1, characterized in that: The neutral layer of the diaphragm structure is located at the center of the diaphragm structure.

9. The MEMS piezoelectric sounder according to claim 4, characterized in that: Each of the first piezoelectric composite layers and each of the second piezoelectric composite layers include, from bottom to top, a bottom electrode layer, an intermediate layer and a top electrode layer; wherein the intermediate layer is a piezoelectric layer, or the intermediate layer is formed by overlapping and stacking a plurality of piezoelectric layers and a plurality of electrode layers; wherein the upper layer of the bottom electrode layer and the lower layer of the top electrode layer are both piezoelectric layers.

10. A loudspeaker, characterized in that: It comprises at least one MEMS piezoelectric sound generator according to any one of claims 1 to 9, and each MEMS piezoelectric sound generator is arranged in a preset array.

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