Piezoelectric MEMS sounding unit and loudspeaker

Abstract

The utility model provides a piezoelectric MEMS sounding unit and a loudspeaker, each peripheral area of the upper surface of a substrate is provided with a first piezoelectric composite unit, the middle rectangular area of the substrate is provided with a slotted gap, the edge of each diaphragm of a formed diaphragm structure is anchored, a gap structure is arranged between every two adjacent first piezoelectric composite units, and the first piezoelectric composite units and the second piezoelectric composite units are arranged in the slotted gap. The internal stress of each diaphragm layer in the diaphragm structure of the piezoelectric MEMS sound production unit due to the process can be reduced by arranging the slotting gap; the flexible material is adopted to cover the slotting gap, the flexibility of the vibrating diaphragm structure can be improved, meanwhile, sound leakage of the piezoelectric MEMS sound production unit at low frequency is reduced, the vibration amplitude and the emission sound pressure level are improved, the flexible material with low density is adopted to replace a silicon vibrating diaphragm with high density, the quality of the vibrating diaphragm structure is reduced, and the cost is reduced. The flexible material reduces the quality factor Q of the resonance of the device, and is beneficial to improving a sound pressure level SPL frequency response curve and a THD frequency response curve, thereby improving the tone quality of the piezoelectric MEMS sound production unit.

Description

Technical Field

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

[0002] In order to make MEMS (Micro-Electro-Mechanical System) sound devices and speakers more widely used, the industry is committed to designing piezoelectric MEMS sound units with high yield, small size and high sound pressure level. However, it is often difficult to balance the small size and high sound pressure level output of devices based on silicon substrates and piezoelectric film materials. In addition, the damping of the piezoelectric MEMS sound unit 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 THD (Total Harmonic Distortion) frequency response curve, resulting in poor sound quality of the piezoelectric MEMS sound unit. In addition, the piezoelectric MEMS sound unit in the related art pushes a small amount of air, which reduces the output sound pressure level SPL of the piezoelectric MEMS sound unit 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 piezoelectric MEMS sound unit and a speaker 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 piezoelectric MEMS sound unit.

[0004] The utility model provides a piezoelectric MEMS sound unit, comprising: a substrate; a first piezoelectric composite unit is respectively arranged in each peripheral area of ​​the upper surface of the substrate; the bottom central area of ​​the substrate has a cavity, and at least a part of each of the first piezoelectric composite units is located in the upper area of ​​the substrate; the upper area is the area corresponding to the orthographic projection of the cavity to the upper surface of the substrate; a slotted gap is arranged in the middle rectangular area of ​​the upper area except for at least a part of each of the first piezoelectric composite units, and the slotted gap is covered with a flexible material, and the upper area of ​​the substrate with the flexible material forms a diaphragm structure of the piezoelectric MEMS sound unit; each diaphragm edge of the diaphragm structure is anchored, and a gap structure is provided between the first piezoelectric composite units of each two adjacent peripheral areas.

[0005] Furthermore, at least one second piezoelectric composite unit is provided in the upper area of ​​the substrate; a slotted gap is provided on each of the second piezoelectric composite units, and / or a slotted gap is provided in the area other than each of the second piezoelectric composite units in the middle rectangular area; and the slotted gap is covered with a flexible material.

[0006] Furthermore, the slotted gap includes: at least one slotted structure of a preset shape; if the width dimension of the slotted structure is between 0.5μm and 5μm, the preset shape includes at least one of the following: a straight line, a circle, a square or a polygon; if the width dimension of the slotted structure is between 10μm and 200μm, the preset shape includes at least one of the following: a circle, a square, a ring or a polygon.

[0007] Furthermore, the aspect ratio of the diaphragm structure is greater than or equal to a preset value; as the aspect ratio of the diaphragm structure increases, the value of the first-order resonance frequency of the piezoelectric MEMS sound unit increases, and the difference between each order resonance frequency decreases.

[0008] Furthermore, the thickness of the diaphragm structure ranges from 0.1 μm to 50 μm; as the thickness of the diaphragm structure increases, the value of the first-order resonance frequency increases.

[0009] Furthermore, each first piezoelectric composite unit and each second piezoelectric composite unit are electrically isolated by an insulating layer and electrically connected by a metal wire.

[0010] Furthermore, each of the first piezoelectric composite units and each of the second piezoelectric composite units 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.

[0011] Furthermore, the thickness of each piezoelectric layer is in the range of 0.1 μm to 25 μm, the thickness of each electrode layer is in the range of 0.01 μm to 5 μm, the thickness of different piezoelectric layers are the same or different, and the thickness of different electrode layers are the same or different.

[0012] Furthermore, at least one rectangular slot is provided on each first piezoelectric composite unit.

[0013] The utility model provides a loudspeaker, comprising at least one piezoelectric MEMS sound generating unit as described in any one of the above items, and each piezoelectric MEMS sound generating unit is arranged in a preset array form.

[0014] The utility model provides a piezoelectric MEMS sound unit and a loudspeaker, wherein the piezoelectric MEMS sound unit comprises: a substrate; a first piezoelectric composite unit is respectively arranged in each peripheral area of ​​the upper surface of the substrate; a cavity is provided in the bottom central area of ​​the substrate, and at least a part of each first piezoelectric composite unit is located in the upper area of ​​the substrate; the upper area is an area corresponding to the orthographic projection of the cavity to the upper surface direction of the substrate; a slotted gap is provided in the middle rectangular area of ​​the upper area except for at least a part of each first piezoelectric composite unit, and the slotted gap is covered with a flexible material, and the upper area of ​​the substrate with the flexible material forms a diaphragm structure of the piezoelectric MEMS sound unit; each diaphragm edge of the diaphragm structure is anchored, and a gap structure is provided between the first piezoelectric composite units of each two adjacent peripheral areas. By setting slotted gaps, the internal stress of each membrane layer in the diaphragm structure of the piezoelectric MEMS sound unit caused by the process can be reduced; by covering the slotted gaps with flexible materials, the flexibility of the diaphragm structure can be improved, while reducing the sound leakage of the piezoelectric MEMS sound unit at low frequencies, increasing the vibration amplitude and the emission sound pressure level, and by replacing the high-density silicon diaphragm with low-density flexible materials, the mass of the diaphragm structure is reduced, and the flexible material reduces the quality factor Q of the device resonance, 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 piezoelectric MEMS sound unit. 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 piezoelectric MEMS sound generating unit provided in an embodiment of the utility model;

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

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

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

[0024] Figure 9(a) , 9(b) A schematic diagram of polarization mode and electrical connection of a piezoelectric MEMS sound generating unit 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) , 12(c) is a schematic diagram of an array arrangement provided in 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 the arrangement of a piezoelectric MEMS sound unit array 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 a simulation result provided by an embodiment of the utility model;

[0031] FIG15( a ) is a schematic diagram of a piezoelectric MEMS speaker provided by an embodiment of the present invention;

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

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

[0037] Fig. 20 A schematic cross-sectional view of a patterned top piezoelectric layer and a middle electrode layer provided in an embodiment of the utility model;

[0038] Fig.21 A schematic cross-sectional view of a bottom piezoelectric layer and a bottom electrode layer after being patterned provided in an embodiment of the utility model;

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

[0040] Fig.23 A schematic cross-sectional view of a metal wire after deposition and patterning provided by an embodiment of the utility model;

[0041] Fig.24 A schematic cross-sectional view of a passivation layer after deposition and patterning provided by an embodiment of the utility model;

[0042] Fig.25 A schematic cross-sectional view of an SOI top silicon trench after etching provided by an embodiment of the utility model;

[0043] Fig.26A schematic cross-sectional view of a device coated with a flexible film material provided in an embodiment of the utility model. DETAILED DESCRIPTION

[0044] 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.

[0045] 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.

[0046] 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 is faster and more accurate than the voice coil, resulting in higher bandwidth and more accurate high-frequency reproduction. This means that a single MEMS speaker can be used for the entire audible frequency range, rather than using multiple speaker units to form a sound-generating system within the full frequency range of 20Hz-20kHz. MEMS speakers usually produce sound by driving air vibrations with one or more actuator diaphragms. Conventional MEMS speakers reach their maximum displacement at the resonant frequency, which results in an unacceptably high amplitude spike in the sound pressure level of the speaker at the resonant frequency, and a smaller frequency domain bandwidth, which deteriorates the frequency response curve.

[0047] In order to make MEMS sound-generating devices and speakers more widely used, the industry is committed to designing MEMS devices with high yield, small size and high sound pressure level. However, since devices based on silicon substrates and piezoelectric film materials often have difficulty in taking both small size and high sound pressure level output into account, the small size of MEMS devices means a small effective driving diaphragm area, and the resonant frequency of the device is generally large. Therefore, how to meet the application needs of wired headphones, TWS (True Wireless Stereo), hearing aids and other fields in a smaller size is a problem that needs to be solved at present.

[0048] 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 limitations 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, and the use of a slotted cantilever beam structure is prone to air leakage due to low-frequency vibration of the diaphragm.

[0049] In another implementation of the related art, a MEMS piezoelectric speaker is provided, which includes: a substrate having a cavity; a vibration structure including a structural layer, a piezoelectric composite layer and a flexible layer; the structural layer includes a structural plate, a structural fixing portion and a plurality of structural springs having slits; the piezoelectric composite layer includes a piezoelectric film and a first electrode layer and a second electrode layer; wherein the areas where the piezoelectric film, the first electrode layer and the second electrode layer overlap in their respective orthographic projections to the substrate serve as piezoelectric drive functional areas, and the flexible layer is spaced apart from the structural layer in the stacking direction of the layers of the vibration structure and its orthographic projection completely covers the slits of the plurality of structural springs. However, the multiple structural spring structures in this manner have poor stability, and impact and falling may cause the spring structure to be damaged. In addition, in the stacking direction of the layers of the vibration structure, due to the mismatch in thermal expansion coefficients between materials, thermal stress is easily present during the manufacturing process in the flexible layer, resulting in device damage.

[0050] 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 addition, the piezoelectric MEMS sound unit pushes a small amount of air, which reduces the output sound pressure level SPL of the piezoelectric MEMS sound unit under excitation, and also affects the sound pressure level SPL frequency response curve, reducing the mid-frequency performance. 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.

[0051] To facilitate understanding of the present embodiment, a piezoelectric MEMS sound unit disclosed in the embodiment of the present utility model is first introduced, and the piezoelectric MEMS sound unit includes: a substrate; a first piezoelectric composite unit is respectively arranged in each peripheral area of ​​the upper surface of the substrate; the bottom central area of ​​the substrate has a cavity, and at least a part of each first piezoelectric composite unit is located in the upper area of ​​the substrate; the upper area is the area corresponding to the orthographic projection of the cavity to the upper surface of the substrate; a slotted gap is arranged in the middle rectangular area of ​​the upper area except for at least a part of each first piezoelectric composite unit, and the slotted gap is covered with a flexible material, and the upper area of ​​the substrate with the flexible material forms a diaphragm structure of the piezoelectric MEMS sound unit; each diaphragm edge of the diaphragm structure is anchored, and a gap structure is provided between the first piezoelectric composite units of each two adjacent peripheral areas.

[0052] 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 peripheral areas. For example, if the upper surface of the substrate is rectangular, the first piezoelectric composite units can be respectively arranged on the four peripheries of the upper surface of the substrate, and the first piezoelectric composite units of the four peripheries can be separated from each other and / or interconnected, and the first piezoelectric composite units on the left and right sides are opposite to each other, and the first piezoelectric composite units on the upper and lower sides are opposite to each other; the piezoelectric MEMS sound unit can perform electroacoustic conversion through the first piezoelectric composite unit, and a driving signal is applied to the first piezoelectric composite unit. The composite layer unit can deform the diaphragm structure under the drive of an electrical signal, thereby generating sound waves and realizing the vibration and sound generation of the piezoelectric MEMS sound unit; 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 piezoelectric MEMS sound unit 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 piezoelectric MEMS sound unit. For cavity shapes such as square, circular, and hexagonal, the larger the size of the cavity, the lower the first-order resonant frequency of the piezoelectric MEMS sound unit. The size here can refer to measurement parameters such as cavity area, length, width, radius or diameter.

[0053] 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 unit is located in the upper area. In the range of the upper area, the middle rectangular area except for a part of each first piezoelectric composite unit is provided with a slotted gap, and the shape and number of the slotted gap 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 Isobutylether, 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 2um to 5μm, the flexible material can not only cover the slotted gap, 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 the slotted gap, the length and width dimensions covered are usually larger than the length and width dimensions of the slotted gap, each diaphragm edge of the diaphragm structure is anchored, and a gap structure is provided between the first piezoelectric composite units of each two adjacent peripheral regions.

[0054] 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.

[0055] The upper area of ​​the substrate with flexible material forms the diaphragm structure of the piezoelectric MEMS sound unit. Usually, the upper surface of the substrate is parallel to the diaphragm structure. 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), polyethyleneterephthalate (PET)), organic or inorganic compounds, any suitable material or a combination thereof.

[0056] like Figure 1 The structure diagram of a piezoelectric MEMS sound generating unit shown in the figure is a schematic diagram of the structure of a piezoelectric MEMS sound generating unit, which is explained by taking the substrate made of SOI material as an example, 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 unit, a bottom piezoelectric layer 09 and a top piezoelectric layer 10 of the first piezoelectric composite unit; the groove area etched on the SOI top silicon 03 is a rectangular groove 16 (corresponding to the above-mentioned grooved gap), and the rectangular groove 16 is located above the hollow area of ​​the cavity 15, which can be obtained by DRIE (Deep Reactive Ion The rectangular groove 16 is obtained by a process of deep reactive ion etching (DERE). The length and width of the rectangular groove 16 are smaller than the design size of the bottom cavity, and the length and width are usually within the range of 100μm to 5000μm. The rectangular groove 16 can also divide two or more mutually unconnected rectangles or other structural figures, such as circles, squares, etc. The rectangular groove 16 can release the process internal stress of each membrane layer, and at the same time reduce the mass of the diaphragm, so that a larger driving displacement and sound pressure level output can be obtained. The flexible material 17 covers the rectangular groove 16. The length and width of the flexible material 17 are larger than the length and width of the rectangular groove 16, but does not cover the first piezoelectric composite unit around the rectangular groove 16. The driving part of the piezoelectric MEMS sound unit is composed of SOI top silicon 03 and the first piezoelectric composite unit. When a piezoelectric driving signal is applied to the electrode layer of the first piezoelectric composite unit, the piezoelectric layer performs a telescopic movement, so that the lower silicon film produces an up and down reciprocating motion, driving the flexible film to vibrate and sound together. The insulating layers 11 and 14 can play the role of electrical insulation, isolation protection, etc. The welding pads 12 and 13 are both connection points of the signal input end, and can be connected to the first piezoelectric composite unit of the piezoelectric MEMS sound unit through metal wiring.

[0057] like Figure 2 A schematic diagram of the structure of a piezoelectric MEMS sound unit 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 piezoelectric MEMS sound unit 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 piezoelectric MEMS sound unit substantially moves along the Y-axis direction.

[0058] like Figure 2 As shown, the piezoelectric MEMS sound unit D10 includes a diaphragm structure, and left, right, and upper and lower first piezoelectric composite units 10a, 10b, 10c, and 10d of the diaphragm structure, wherein the left and right first piezoelectric composite units 10a and 10c are respectively connected to the edges 30a and 30c anchored to the piezoelectric MEMS sound unit D10, and the upper and lower first piezoelectric composite units 10b and 10d are respectively connected to the edges 30b and 30d anchored to the piezoelectric MEMS sound unit D10, and are fixed on the substrate of the piezoelectric MEMS sound unit D10. 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 piezoelectric MEMS sound unit D10. The cavity area can be obtained by a back etching process or other methods, so that the diaphragm structure vibrates on the piezoelectric MEMS sound unit D10 and deviates. The outer edges of the left and right first piezoelectric composite units 10a and 10c, and the upper and lower first piezoelectric composite units 10b and 10d exceed the edge of the back cavity of the piezoelectric MEMS sound unit D10. The gap 40e is a rectangular groove, the length and width of which are smaller than the length and width of the cavity on the back of the piezoelectric MEMS sound unit D10, and the rectangular groove can also divide two or more unconnected rectangles or other structural figures, such as circles, squares, etc. The rectangular groove is covered with a flexible material 70a, and the length and width of the flexible material 70a are larger than the length and width of the rectangular groove. The rectangular groove removes the silicon material of the diaphragm structure and covers it with a flexible dry film, which can reduce the stiffness of the piezoelectric MEMS sound unit and reduce the mass of the diaphragm structure, which is conducive to improving the sound pressure level curve and improving the mid-frequency performance.

[0059] The above-mentioned piezoelectric MEMS sound unit can reduce the internal stress of each membrane layer in the diaphragm structure of the piezoelectric MEMS sound unit caused by the process by setting the slotted gaps; the slotted gaps are covered with flexible materials, which can improve the flexibility of the diaphragm structure, while reducing the sound leakage of the piezoelectric MEMS sound unit at low frequencies, and increasing the vibration amplitude and the emission sound pressure level. 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 flexible material reduces the quality factor Q of the device resonance, 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 piezoelectric MEMS sound unit.

[0060] Furthermore, at least one second piezoelectric composite unit is provided in the upper region of the substrate; a slotted gap is provided on each second piezoelectric composite unit, and / or a slotted gap is provided in the middle rectangular region except for each second piezoelectric composite unit; and the slotted gap is covered with a flexible material.

[0061] In actual implementation, one or more second piezoelectric composite units can be set in the middle of the upper area of ​​the substrate, which can also be understood as one or more second piezoelectric composite units can be set in the middle of the diaphragm structure of the piezoelectric MEMS sound unit. A slotted gap can be set on each second piezoelectric composite unit, or a slotted gap can be set around the second piezoelectric composite unit in the middle rectangular area. The specific selection can be based on actual needs, and the slotted gap is covered with a flexible material, and the length and width of the covering are usually larger than the length and width of the slotted gap. In actual implementation, the second piezoelectric composite unit in the central area can also be divided into two or more parts, and its shape can be circular, hexagonal, octagonal or other irregular graphic structures.

[0062] In actual implementation, the slotted gap may run through the entire diaphragm structure to divide the diaphragm structure into two parts to form a cantilever beam structure, or a part may be left to form a connecting lock structure so that the diaphragm structure vibrates uniformly when driven.

[0063] When the size of the slot is relatively small, it penetrates the diaphragm structure in the thickness direction and is the thickness of the diaphragm structure. When the width of the slot is less than 15μm, it is covered with a flexible material, which is helpful to prevent sound leakage. When the width of the slot is less than 5μm, the diaphragm structure vibrates and makes sound. When the sound propagates in the narrow gap, 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 loss at low frequencies.

[0064] When the size of the slot is relatively large, it penetrates the diaphragm structure in the thickness direction and is the thickness of the diaphragm structure. When the width of the slot is between 5μm and 2000μm, the diaphragm structure formed in combination with the rigid material can improve the flexibility of the diaphragm structure, while reducing the sound leakage of the piezoelectric MEMS sound generating unit at low frequencies, and increasing the vibration amplitude and emission sound pressure level of the piezoelectric MEMS generating unit. When the size of the slot is relatively large, 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.

[0065] The quality factor Q of the resonance of the piezoelectric MEMS sound unit is usually relatively large, and after the excitation is applied, its displacement frequency curve or 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 smooth and reducing the total harmonic interference THD.

[0066] Furthermore, the slotted gap includes: at least one slotted structure of a preset shape; if the width dimension of the slotted structure is between 0.5μm and 5μm, the preset shape includes at least one of the following: a straight line, a circle, a square or a polygon; if the width dimension of the slotted structure is between 10μm and 200μm, the preset shape includes at least one of the following: a circle, a square, a ring or a polygon.

[0067] In actual implementation, the slotted gap may include one or more slotted structures. If there are multiple slotted structures, the sizes of the multiple slotted structures may be the same or different, and the shapes may be the same or different. Specifically, a suitable shape may be selected according to the width size of the slotted structure, or the slot may not be completely opened.

[0068] Furthermore, the aspect ratio of the diaphragm structure is greater than or equal to a preset value; as the aspect ratio of the diaphragm structure increases, the value of the first-order resonance frequency of the piezoelectric MEMS sound unit increases, and the difference between each order resonance frequency decreases.

[0069] In the present embodiment, the diaphragm structure is a rectangular structure. For example, the left and right anchoring edges are the length of the diaphragm structure, while the upper and lower anchoring edges are the width of the diaphragm structure. The aspect ratio is greater than or equal to 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 piezoelectric MEMS sound unit are closely related to the resonant frequency of the piezoelectric MEMS sound unit. The length and width of the rectangular diaphragm structure will affect the resonant frequency of the piezoelectric MEMS sound unit, wherein the smaller the diaphragm width, the higher the resonant frequency can be obtained. The diaphragm length of the piezoelectric MEMS sound unit affects the output sound pressure level of the device. A piezoelectric MEMS sound unit with a large aspect ratio can achieve a higher resonant frequency and a larger sound pressure level SPL than a piezoelectric MEMS sound unit with a small aspect ratio. Figure 2 Taking the piezoelectric MEMS sound unit D10 in the example, the aspect ratio of the diaphragm structure of the piezoelectric MEMS sound unit D10 can be greater than 3 or other. The smaller the difference between the resonance frequencies of each order of the piezoelectric MEMS sound unit D10, the mixed resonance can be achieved when the quality factor Q of the resonance of the piezoelectric MEMS sound unit D10 is reduced. A plurality of piezoelectric MEMS sound units D10 are used to form an array structure, so that a plurality of relatively wide-band smooth peaks can be mixed together to form a frequency response that is relatively flat to the resonance frequency, so as to improve the performance of the piezoelectric MEMS sound unit D10. By applying a drive to the first piezoelectric composite unit 10a, 10b, 10c, and 10d, 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 unit corresponds to the output sound wave signal, corresponding to the input drive signal. The audio drive signal is generally a sinusoidal signal of DC voltage plus AC voltage, such as 10VDV+10VP; or driven by a bipolar signal. The diaphragm structure of the piezoelectric MEMS sound unit D10 is a rectangular structure. The width of the diaphragm structure significantly affects the first-order resonant frequency of the piezoelectric MEMS sound unit 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 aspect ratio in the structural design of the piezoelectric MEMS sound unit is generally relatively large.

[0070] Furthermore, the thickness range of the diaphragm structure is 0.1 μm to 50 μm; as the thickness of the diaphragm structure is thicker, the value of the first-order resonance frequency is larger.

[0071] 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 piezoelectric MEMS sound unit design. For example, when the piezoelectric MEMS sound unit and the cavity size are determined, if the first-order resonant frequency of the piezoelectric MEMS sound unit is required to be lower, a diaphragm structure with a thinner thickness is usually selected. If the first-order resonant frequency of the piezoelectric MEMS sound unit is required to be higher, a diaphragm structure with a thicker thickness is usually selected. The first-order resonant frequency of the piezoelectric MEMS sound unit 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 piezoelectric MEMS sound unit are certain, generally speaking, the thinner the thickness of the diaphragm structure, the lower the first-order resonant frequency of the piezoelectric MEMS sound unit. When the piezoelectric MEMS sound unit and the cavity size of the piezoelectric MEMS sound unit 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 piezoelectric MEMS sound unit are. Under the same piezoelectric drive, the greater the deflection displacement of the diaphragm structure, the greater the amount of air pushed out, and the higher the output sound pressure level.

[0072] Furthermore, each first piezoelectric composite unit and each second piezoelectric composite unit are electrically isolated by an insulating layer and electrically connected by a metal wire.

[0073] The metal wires can be gold wires, copper wires, aluminum wires, etc. In actual implementation, the multiple first piezoelectric composite units outside the four peripheries of the diaphragm structure and each second piezoelectric composite unit inside the diaphragm structure can be electrically isolated by an insulating layer, and then electrically connected by metal wire routing, mainly according to the polarization direction of the piezoelectric layer in each piezoelectric composite unit. The series and / or parallel connection is made, so that the device outputs the maximum sound pressure level under excitation. Figure 2 As shown, the piezoelectric MEMS sound unit D10 has a plurality of slotted gaps, indicated by white dotted lines 40a, 40b, 40c, 40d, and 40e, wherein the slotted gaps 40a, 40b, 40c, and 40d are respectively between the adjacent unit corners of the first piezoelectric composite units 10a, 10b, 10c, and 10d, so that the first piezoelectric composite units 10a, 10b, 10c, and 10d at the periphery of the piezoelectric MEMS sound unit D10 are separated from each other and are not connected to each other in structure.

[0074] Furthermore, each first piezoelectric composite unit and each second piezoelectric composite unit 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.

[0075] In actual implementation, the first piezoelectric composite unit located on the outer sides of the four peripheries above the diaphragm structure and the second piezoelectric composite unit in the middle can be arranged above and / or below the diaphragm structure; each of the first piezoelectric composite unit and each of the second piezoelectric composite units 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. The application of an electric field to the piezoelectric layer of each piezoelectric composite unit is closely related to the polarization direction of the piezoelectric layer. Reasonable handling of the relationship between the two maximizes the offset of the output of the piezoelectric MEMS sound unit.

[0076] As shown in Fig. 3(a), a schematic diagram of the structure of a piezoelectric composite unit, as shown in Fig. 3(b), and a schematic diagram of the structure of a piezoelectric composite unit, as shown in Fig. 3(c), the piezoelectric composite unit in Fig. 3(a) is a single piezoelectric layer, and the piezoelectric composite unit is respectively a bottom electrode layer, a piezoelectric layer, and a top electrode layer from bottom to top; the piezoelectric composite unit in Fig. 3(b) is a double piezoelectric layer, and the piezoelectric composite unit is respectively: a bottom electrode layer, a piezoelectric layer, an electrode layer, a piezoelectric layer, and a top electrode layer from bottom to top; the piezoelectric composite unit 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 here. According to the number of piezoelectric layers and the polarization direction of the piezoelectric layers in different regions, there are a variety of electrical connection methods. By comparison, the optimal connection method that maximizes the displacement of the diaphragm structure of the piezoelectric MEMS sound unit and outputs the highest sound pressure level can be obtained.

[0077] Furthermore, the thickness of each piezoelectric layer ranges from 0.1 μm to 25 μm, the thickness of each electrode layer ranges from 0.01 μm to 5 μm, the thicknesses of different piezoelectric layers are the same or different, and the thicknesses of different electrode layers are the same or different.

[0078] If the first piezoelectric composite unit and / or the second piezoelectric composite unit 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.

[0079] Similarly, if the first piezoelectric composite unit and / or the second piezoelectric composite unit 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.

[0080] Furthermore, at least one rectangular slot is provided on each first piezoelectric composite unit.

[0081] In actual implementation, one or more rectangular slots can be set on each first piezoelectric composite unit. Each rectangular slot can be set parallel to the X-axis direction, parallel to the Y-axis direction, or set at a certain angle to the X-axis direction or the Y-axis direction. The specific selection can be based on actual needs. The internal stress of the first piezoelectric composite unit caused by the process can be reduced by setting one or more rectangular slots.

[0082] Si material is relatively brittle, and the diaphragm structure that combines PZT (lead zirconate titanate) film and Si film layer is used for the anchoring position of the driver, which can easily cause the diaphragm to crack and break. The diaphragm structure that combines rigidity and flexibility is formed by these flexible dry film materials. When the dry film is subjected to stress, it can buffer and absorb the stress through its own deformation, thereby improving the impact resistance of the piezoelectric MEMS sound unit. And when the cavity structure of the piezoelectric MEMS sound unit is large, the residual stress of the MEMS process will cause the diaphragm structure to bulge or dent. This structure composed of flexible dry film materials can play the role of reinforcing ribs. At the same time, because 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.

[0083] The above-mentioned piezoelectric MEMS sound generating unit includes a diaphragm structure, which is a rectangular reinforced structure. The four outer sides of the diaphragm structure have first piezoelectric composite layer units, and each first piezoelectric composite layer unit includes: a bottom electrode layer, an intermediate layer and a top electrode layer located on the upper side of the diaphragm structure; at the same time, the first piezoelectric composite unit can be arranged above and / or below the diaphragm structure. One side edge of the first piezoelectric composite layer unit outside the four outer sides can be anchored on the device, and the other side edge is located on the diaphragm structure. The anchoring edges on the left and right sides and the upper and lower sides of the diaphragm structure are completely or partially fixed on the device substrate. By polarizing different piezoelectric layers and piezoelectric films in different regions of the same layer, and electrically connecting the first piezoelectric composite unit, the displacement, driving force and output sound pressure level driven by the diaphragm structure of the piezoelectric MEMS generating unit are optimized.

[0084] In actual implementation, in addition to Figure 1 The diaphragm structure in the piezoelectric MEMS sound unit can also be formed in other forms. For example, FIG4(a) shows a schematic diagram of the structure of a piezoelectric MEMS sound unit. The piezoelectric MEMS sound unit D11 is relative to Figure 2 As for the piezoelectric MEMS sound unit D10 in the figure, the second piezoelectric composite unit inside the diaphragm structure of the piezoelectric MEMS sound unit and the speaker has two regions 10e and 10f, and each second piezoelectric composite unit is grooved to form a grooved gap 40e and a grooved gap 40f, respectively, and the grooved gaps 40e and 40f are covered with flexible materials 70a and 70b. The grooved gaps in Figure 4 (a) do not divide the region; but the grooved straight line can also extend to the diaphragm, dividing 10e and 10f into two regions, and the grooved straight line can also be composed of multiple segments.

[0085] As shown in FIG4( b ), there is only one second piezoelectric composite unit in the center of the diaphragm structure of the piezoelectric MEMS sound unit D12, which can be divided into a plurality of regions, and its shape can be rectangular, square, circular, etc.; and the middle slots 40e, 40f, 40g, 40h form a rectangular frame around the outside of the second piezoelectric composite unit inside, and are covered with flexible materials 70a, 70b, 70c, 70d.

[0086] As shown in FIG4(c), a schematic diagram of the structure of a piezoelectric MEMS sound unit is shown. The diaphragm structure of the piezoelectric MEMS sound unit D13 is grooved with grooves 40e, 40f, 40g, and 40h to form a rectangular frame located inside the diaphragm structure, and is covered with a flexible material. The silicon diaphragm with a high density is removed, and a low-density flexible material is used to replace the diaphragm structure, thereby reducing the mass of the diaphragm structure, which is beneficial to improving the sound pressure level curve and the mid-frequency performance. The central etching shape of the diaphragm structure can be a variety of structures, such as two rectangular frame structures, or a circular, square, or polygonal structure. The number and position of the etched groove structure can be various, and are not limited to those shown in the piezoelectric MEMS sound unit D13. The multiple first piezoelectric composite units of the piezoelectric MEMS sound unit D13 also have a plurality of rectangular grooved gaps covered with flexible materials distributed on the device, such as three rectangular grooved gaps on the left and right sides along the X-axis direction, and each grooved gap distributed on the four corners.

[0087] As shown in FIG4(d), a schematic diagram of the structure of a piezoelectric MEMS sound unit, there is only one second piezoelectric composite unit in the center of the diaphragm structure of the piezoelectric MEMS sound unit D14, and slotted gaps 40e and 40f are formed on both sides of the second piezoelectric composite unit, and the two slotted gaps 40e and 40f can be centrally symmetrical.

[0088] The piezoelectric MEMS sound generating unit can be grooved on the second piezoelectric composite unit inside the diaphragm, as shown in FIG4(a); or grooves can be made on the diaphragm, as shown in FIG4(b). Figure 2 As shown, the position of the grooves is not limited to that shown in the figure; a flexible diaphragm, and / or a diaphragm in which rigid and flexible materials are combined with each other can be formed.

[0089] For the above-mentioned piezoelectric MEMS piezoelectric sound generating unit, if a groove is made on the second piezoelectric composite unit inside the diaphragm structure, when the width of the groove gap is between 0.5μm and 5μm, due to the relatively small size, when the sound propagates in the narrow slit, the heat loss and viscosity loss will cause the sound wave to attenuate, and it is not necessary to cover it with a flexible material; when the groove gap is greater than 5μm, it can be covered with a flexible material to prevent sound leakage. For example, in the piezoelectric MEMS piezoelectric sound generating unit D11 in Figure 4(a), the width of the flexible material is greater than the groove gap, and the flexible material can be used to cover all or part of the gap, and can also cover the entire or part of the diaphragm structure.

[0090] As shown in Fig. 4(e), a schematic diagram of the structure of a piezoelectric MEMS sound unit is shown. Compared with the piezoelectric MEMS sound unit D10, the piezoelectric MEMS sound unit D15 does not have a second piezoelectric composite unit inside the diaphragm, and there are four rectangular frames composed of flexible materials 70a, 70b, 70c, and 70d in the middle of the diaphragm, as well as rectangular strips composed of flexible materials 70e, 70f, 70g, and 70h. Such a structure composed of flexible materials mainly serves as a reinforcing rib. Under piezoelectric drive, the resonant frequency of the device can be increased without significantly reducing the maximum excursion of the diaphragm, thereby widening the bandwidth of the piezoelectric MEMS sound unit. The reinforcing rib structure composed of flexible materials is not limited to this, and its structure is diverse and can be set according to actual needs.

[0091] As shown in FIG4(f), a schematic diagram of the structure of a piezoelectric MEMS sound unit, the piezoelectric MEMS sound unit D16, is different from the piezoelectric MEMS sound unit D15. The slotted slits of the piezoelectric MEMS sound unit D16 are located at different positions inside the diaphragm, and there are two slotted slits presenting a centrally symmetrical structure, such as 40e and 40f in the figure, and the slotted slits are covered by flexible materials 70a and 70b. The positions of the slotted slits inside the diaphragm can be different, the number of slotted slits can be multiple, and a centrally aligned structure or other structures can be present. At the same time, the slotted slits can be fully or partially covered with or without a flexible material, and the upper and lower parts of the slotted slits exceed the height of the entire slit, that is, there can be multiple forms such as no coverage, partial coverage, and partial non-coverage.

[0092] As shown in Fig. 4(g), there is no second piezoelectric composite unit inside the diaphragm of the piezoelectric MEMS sound unit D17. The slotted slits 40e and 40f are located on the center straight line inside the diaphragm and have the same size and length, and the two slits are symmetrical about the center horizontal line of the device. The shape of the internal etched slit can be one or more straight lines, circles, S-line segments, elliptical line segments, or various graphic structures such as special shapes. The etching position, the number of etched slits, the size parameters of the etched slits (width, length, radius), etc. can have multiple different structures or combined structures. As shown in Fig. 4(h), there is no etched slit in the piezoelectric MEMS sound unit D18, and there is no flexible material to cover the slit.

[0093] As shown in FIG4(i), a schematic diagram of the structure of a piezoelectric MEMS sound unit is shown. The piezoelectric MEMS sound unit D19 is different from the piezoelectric MEMS sound unit D18. The slotted gap is inside the diaphragm, and there are two slotted gaps and present a symmetrical structure. The left and right slotted gaps are parallel and equal in length. The slotted gap part is completely removed by the MEMS process, and the slotted gap is covered with a flexible material. In addition, the slotted gap inside the diaphragm is a rectangular structure, or it can be composed of one or more graphics such as square, circular, ring, hexagonal or polygonal structures. The size and position of the graphics can be selected according to actual needs. In the piezoelectric MEMS sound unit D19, the entire etched area can be 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 structure can be formed. When the device vibrates, there is no air leakage inside the diaphragm.

[0094] As shown in Figure 4(j), a structural diagram of a piezoelectric MEMS sound unit, the piezoelectric MEMS sound unit D20, is compared with the piezoelectric MEMS sound unit D19. The piezoelectric MEMS sound unit D20 has two rectangular structures inside the diaphragm, and the two rectangular structures have the same size and are symmetrical in the horizontal and vertical axis directions.

[0095] As shown in FIG4(k), a schematic diagram of the structure of a piezoelectric MEMS sound unit, the diaphragm of the piezoelectric MEMS sound unit D21 has six rectangular slots inside, and the six rectangular structures have the same size and are regularly distributed inside the diaphragm. Flexible material is used to cover each of the six rectangular slots, but the various parts are not connected to each other, and the entire flexible material can also be used to cover the six rectangular slots.

[0096] The diaphragm structure of the piezoelectric MEMS sound unit can also be formed in other forms, such as the structural schematic diagram of a piezoelectric MEMS sound unit as shown in Figure 4(m), the structural schematic diagram of a piezoelectric MEMS sound unit as shown in Figure 4(n), the structural schematic diagram of a piezoelectric MEMS sound unit as shown in Figure 4(o), the structural schematic diagram of a piezoelectric MEMS sound unit as shown in Figure 4(p), the structural schematic diagram of a piezoelectric MEMS sound unit as shown in Figure 4(q), and the structural schematic diagram of a piezoelectric MEMS sound unit as shown in Figure 4(r). The shape, position, size, etc. of the appropriate slot can be selected according to actual needs, and are not limited here.

[0097] The piezoelectric MEMS sound unit 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 operating within the linear range of the diaphragm structure, 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.

[0098] The piezoelectric MEMS sound unit in this embodiment has a mechanical resonance point designed to be within the audible sound range of 20Hz-20kHz. When the first-order resonance frequency is 4-10KHz, the diaphragm drive displacement is large under the drive of the piezoelectric signal, and the piezoelectric MEMS sound unit outputs a large sound pressure level in the low-frequency range, which can be used in low-frequency speakers. When the mechanical resonance point of the piezoelectric MEMS sound unit is designed to be greater than 20kHz outside the audible sound, the first and third odd harmonics of the piezoelectric MEMS sound unit are outside the audible sound frequency range, and the piezoelectric MEMS sound unit has low nonlinearity and low THD, which can be used in high-frequency speakers.

[0099] When the piezoelectric polarization modes of the piezoelectric composite units on the outside of the four peripheries and the internal middle area of ​​the piezoelectric MEMS sound unit are consistent, the electrical connection mode of the piezoelectric composite units is parallel; when the piezoelectric polarization modes of the piezoelectric composite units in the middle area are inconsistent, the electrical connection mode of the piezoelectric composite units is divided into series, parallel or series-parallel according to actual conditions.

[0100] The neutral layer of the entire film of the piezoelectric MEMS sound unit 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 units 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.

[0101] When the piezoelectric MEMS sound unit operates at the mechanical resonance point, the thickness of the diaphragm structure and the size of the cavity can be designed within the audio range, or beyond the range of 20KHz, or even in the ultrasonic frequency band.

[0102] Below Figure 2Taking the cross-sectional view of the piezoelectric MEMS sound unit D10 in the embodiment as an example, a polarization mode and electrical connection schematic diagram of a piezoelectric MEMS sound unit as shown in FIG5(a), a polarization mode and electrical connection schematic diagram of a piezoelectric MEMS sound unit as shown in FIG5(b), a polarization mode and electrical connection schematic diagram of a piezoelectric MEMS sound unit as shown in FIG5(c), and a polarization mode and electrical connection schematic diagram of a piezoelectric MEMS sound unit as shown in FIG5(d) are provided. There are first piezoelectric composite units 10a and 10c on the left and right sides of the piezoelectric MEMS sound unit D10, and there is no second piezoelectric composite unit in the center of the diaphragm structure. As shown in FIG5(a), FIG5(b), FIG5(c), and FIG5(d), the direction of the arrow indicating the piezoelectric layer in the piezoelectric composite units 10a and 10c (upward or downward along the Z-axis direction) is the polarization direction of the piezoelectric layer of the device, and the positive and negative symbols in the top electrode layer, the middle electrode layer, and the bottom electrode layer in the piezoelectric composite units 10a and 10c represent the positive and negative electrodes. As shown in FIG5(a), the polarization directions of all piezoelectric layers of the piezoelectric MEMS sound unit are consistent and upward. In terms of electrical connection, the middle electrode layers of the piezoelectric composite units 10a and 10c are connected to the negative, and the top electrode layer and the bottom electrode layer are connected in parallel to the positive. The piezoelectric composite units 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 units 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 units 10a and 10c are different. For example, in FIG5(b), the polarization directions of the upper and lower piezoelectric layers in the piezoelectric composite units 10a and 10c are both downward, in FIG5(c), the polarization direction of the bottom piezoelectric layer in the piezoelectric composite units 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 units 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 electrode of each piezoelectric composite unit 10a and 10c is connected to the negative electrode, and the top electrode layer and the bottom electrode layer are connected in parallel to the positive electrode. The electrical connection between the piezoelectric composite units 10a and 10c is 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 units 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] The following provides a schematic diagram of the simulation results of a piezoelectric MEMS sound unit as shown in Figure 6(a), a schematic diagram of the simulation results of a piezoelectric MEMS sound unit as shown in Figure 6(b), a schematic diagram of the simulation results of a piezoelectric MEMS sound unit as shown in Figure 6(c), and a schematic diagram of the simulation results of a piezoelectric MEMS sound unit as shown in Figure 6(d), which correspond to four displacement diagrams of the diaphragm structure of the piezoelectric MEMS sound unit under four different polarization modes, respectively. The maximum displacements obtained by simulation are: -5.02um, 5.02um, -18.3um, 18.3um, and by comparing the displacement performance of the devices, it can be seen that when the middle electrode layer is grounded and the top electrode layer and the bottom electrode layer are connected in parallel, the polarization directions of the upper and lower piezoelectric layers of the piezoelectric composite unit are opposite, that is, the maximum displacement can be obtained in the cases of Figure 5(c) and Figure 5(d).

[0105] In FIG. 5(a) and FIG. 5(b), the arrows indicating the upper and lower piezoelectric layers in the piezoelectric composite units 10a and 10c are all upward or all downward along the Z-axis direction. In order to make the performance of the piezoelectric MEMS sound unit have a good displacement as shown in FIG. 5(c) and FIG. 5(d), the electrical connection mode of the piezoelectric composite units 10a and 10c can be changed, as shown in FIG. 7(a) of a piezoelectric MEMS sound unit polarization mode and electrical connection schematic diagram, and as shown in FIG. 7(b) of a piezoelectric MEMS sound unit polarization mode and electrical connection schematic diagram, in terms of electrical connection: the middle electrode layer of each of the piezoelectric composite units 10a and 10c is grounded, 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 units 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 units 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 18.3μm, 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] Taking the piezoelectric MEMS sound unit D19 in FIG. 4(i) as an example, the following provides a polarization mode and electrical connection schematic diagram of a piezoelectric MEMS sound unit as shown in FIG. 8(a), a polarization mode and electrical connection schematic diagram of a piezoelectric MEMS sound unit as shown in FIG. 8(b), a polarization mode and electrical connection schematic diagram of a piezoelectric MEMS sound unit as shown in FIG. 8(c), and a polarization mode and electrical connection schematic diagram of a piezoelectric MEMS sound unit as shown in FIG. 8(d). In FIG. 8(a), FIG. 8(b), FIG. 8(c), and FIG. 8(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 units 10a and 10c in FIG. 8(a) and FIG. 8(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 units 10a, 10b, and 10c represent positive and negative electrodes. As shown in FIG8(a), the piezoelectric MEMS sound generating unit is electrically connected to the ground of the intermediate electrode layers of the piezoelectric composite units 10a, 10b, and 10c, and the top electrode layer and the bottom electrode layer are connected in parallel to the positive electrode. The piezoelectric composite units 10a, 10b, and 10c in FIG8(a) are electrically connected to the ground, and the positive electrode is connected to the positive electrode. The connection mode of the three piezoelectric composite units 10a, 10b, and 10c is a parallel structure; the top electrode layer of the piezoelectric composite unit 10b in FIG8(b) is connected to the positive electrode, and the bottom electrode layer is connected to the negative electrode. The polarity can be reversed, that is, the top electrode layer is connected to the negative electrode, and the bottom electrode layer is connected to the positive electrode. The piezoelectric composite units 10a and 10c in FIG8(b) are electrically connected to the ground, the positive electrode is connected to the positive electrode, and the negative electrode is connected to the negative electrode. The connection mode between the piezoelectric composite units 10a, 10b, and 10c is a series structure.

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

[0108] As shown in Figure 9(a), a schematic diagram of the polarization mode and electrical connection of a piezoelectric MEMS sound unit, and as shown in Figure 9(b), a schematic diagram of the polarization mode and electrical connection of a piezoelectric MEMS sound unit, the arrows indicating the upper and lower piezoelectric layers in the piezoelectric composite units 10a, 10b, and 10c are all pointing upward or downward along the Z-axis direction. In Figure 9(a), the arrows indicating the upper and lower piezoelectric layers in the piezoelectric composite units 10a, 10b, and 10c are all pointing upward along the Z-axis direction, or the arrows of 10a, 10b, and 10c are all pointing in opposite directions, and the direction of the arrow is the polarization direction of the piezoelectric layer of the device. In order to achieve the optimal maximum displacement of device performance, the electrical connection method of device D19 is shown in Figures 9(a) and 9(b). In Figure 9(a), the polarization direction of each voltage layer is upward or downward. In terms of electrical connection, the middle layer electrodes of the piezoelectric composite units 10a and 10c are grounded, and the upper and lower electrode layers are respectively connected to electrical positive and negative, or the upper and lower electrode layers are respectively connected to electrical negative and positive, while the piezoelectric composite unit 10b is exactly the opposite of 10a and 10c. Then the piezoelectric composite units 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 units 10a and 10c is a parallel structure, and the connection between the piezoelectric composite units 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 units 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 units 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 units 10a, 10b, and 10c is a parallel structure. When the arrows of the piezoelectric composite units 10a, 10b, and 10c point to opposite directions and the polarization directions are changed, the connection mode between the three piezoelectric composite units 10a, 10b, and 10c is still a parallel structure, but the displacements obtained 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 unit represent positive and negative electrodes. When the polarity of the top electrode layer and the bottom electrode layer of the same piezoelectric composite unit 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 unit, and there are two or more piezoelectric composite units on the diaphragm structure, the performance of the device is related to the polarization direction of the piezoelectric layer of the piezoelectric composite unit 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] The above-mentioned piezoelectric MEMS sound unit can increase the amount of air pushed by the piezoelectric MEMS sound unit, increase the sound pressure level SPL output by the piezoelectric MEMS sound unit under excitation, and improve the device sound pressure level SPL frequency curve, and improve the mid-frequency performance. It can also increase the frequency bandwidth of the piezoelectric MEMS sound unit, not only can it output a higher sound pressure level in the full frequency band (20Hz-20kHz), but also has better acoustic performance in the ultrasonic range beyond 20kHz, thereby enhancing the performance of the device.

[0111] An embodiment of the utility model provides a speaker, comprising at least one piezoelectric MEMS sound generating unit according to any one of the above items, and each piezoelectric MEMS sound generating unit is arranged in a preset array form.

[0112] 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 with a single piezoelectric MEMS sound unit has a limited output sound pressure level SPL under excitation, multiple piezoelectric MEMS sound units can be distributed in an array structure to increase the sound area of ​​the speaker, 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).

[0113] Figure 10(a) uses the same structure of piezoelectric MEMS sound units, and the size parameters, structural shapes, and performance of the unit devices 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 piezoelectric MEMS sound unit 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 1x1, 2x2, 3x3, 2x3, 3x2, 4x4 and other array structures. In the array structure, the piezoelectric MEMS sound unit D10 may be used, and other piezoelectric MEMS sound units, such as the piezoelectric MEMS sound unit D11, the piezoelectric MEMS sound unit D12, etc., may also be used to form an array structure of multiple identical devices.

[0114] 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 piezoelectric MEMS sound unit D11 is arranged as 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 piezoelectric MEMS sound unit D12 is arranged as 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 piezoelectric MEMS sound unit D11 and the piezoelectric MEMS sound unit D12 can be arranged in a variety of different array structures such as 2x2, 3x3, 4x4, 2x3, 3x2, etc. Other piezoelectric MEMS sound units can also be used in the array structure, such as piezoelectric MEMS sound unit D14 and / or piezoelectric MEMS sound unit D15.

[0115] The array structure layout in Figure 10(c) has a linear arrangement of the horizontal and vertical axes. The piezoelectric MEMS sound unit D14 is arranged in a single or multiple units in the horizontal axis X direction, and the piezoelectric MEMS sound units in the horizontal axis X direction are different; the piezoelectric MEMS sound unit D13 is arranged in a single or multiple units in the vertical axis Y direction, and the piezoelectric MEMS sound units in the vertical axis Y direction are different; the horizontal and vertical axes can be arranged linearly at the same time, using the piezoelectric MEMS sound unit D14 and the piezoelectric MEMS sound unit D16, the piezoelectric MEMS sound unit D13 and the piezoelectric MEMS sound unit 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 piezoelectric MEMS sound units of the array can be other piezoelectric MEMS sound units, such as the piezoelectric MEMS sound unit D17 and / or the piezoelectric MEMS sound unit D20.

[0116] Of course, other array arrangements can also be selected according to actual needs, such as an array arrangement schematic diagram shown in FIG11(a), an array arrangement schematic diagram shown in FIG11(b), an array arrangement schematic diagram shown in FIG11(c), an array arrangement schematic diagram shown in FIG12(a), an array arrangement schematic diagram shown in FIG12(b), and an array arrangement schematic diagram shown in FIG12(c). Figure 13(a) , 13(b) , 13(c), 13(d), 13(e), 13(f), 13(g), and 13(h) are schematic diagrams of the arrangement of a piezoelectric MEMS sound unit array. A suitable arrangement can be selected according to actual needs and is not limited here.

[0117] In this embodiment, when used as a loudspeaker, depending on the size of the emitted sound pressure level, the loudspeaker can be a single piezoelectric MEMS sound unit, or it can be a plurality of piezoelectric MEMS sound units arranged in a preset array and driven by electrical parallel to increase the output sound pressure level, wherein the diaphragm structures of the plurality of piezoelectric MEMS sound units are coplanar.

[0118] 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.

[0119] If the polarization directions of the piezoelectric layers in all the piezoelectric MEMS sound units 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 piezoelectric MEMS sound units 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.

[0120] The piezoelectric MEMS sound generating unit and speaker of the embodiment of the utility model can be used as a MEMS actuator, specifically a piezoelectric MEMS driver, a piezoelectric MEMS micro pump, a piezoelectric MEMS micro mirror, a piezoelectric MEMS switch, 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.

[0121] The structure of the above-mentioned loudspeaker is verified below. A schematic diagram of a loudspeaker as shown in FIG14(a) is a MEMS loudspeaker device A having an array structure composed of four square units. A schematic diagram of a piezoelectric MEMS loudspeaker as shown in FIG15(a) is a MEMS loudspeaker device B having an array structure composed of three rectangular units reinforced on four sides. MEMS loudspeaker devices A and B of 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. As shown in Figures 14(b) and 14(c), the simulation results of device A are shown; as shown in Figures 15(b) and 15(c), the simulation results of device B are shown; it can be seen from the figure that the resonant frequencies of the unit structures of MEMS speaker A and MEMS speaker B are 8.92kHz and 11.0kHz respectively, and the maximum displacements are 50.1um and 42.9um respectively. By integrating the displacement of the device diaphragm, the volume of air pushed by the corresponding MEMS speaker A and MEMS speaker B is 0.469mm^3 and 0.509mm^3. By comparing MEMS speaker A and MEMS speaker B, the first-order resonant frequency of the single unit simulation of MEMS speaker B and MEMS speaker A is close, but the maximum displacement of the diaphragm of MEMS speaker B device is much larger under voltage drive, 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.

[0122] The above-mentioned piezoelectric MEMS sound unit has a gap for mechanical decoupling. When the width of the slot is 0.5μm to 5μm, 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, while reducing the sound leakage of the device at low frequencies, and improving the vibration amplitude and emission sound pressure level of the MEMS piezoelectric sound unit. When the width of the slot 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.

[0123] The piezoelectric MEMS sound unit is a rectangular structure. Compared with the circular and square sound units, the 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.

[0124] Based on a double-layer piezoelectric PZT film, and through reasonable polarization of the piezoelectric layer and electrical connection of different regions, the dual driving electrodes (inner and outer electrodes) use a piston mode with a 180° anti-phase driving structure to improve the emission sound pressure level of the piezoelectric MEMS sound unit and speaker.

[0125] This embodiment adopts a rectangular diaphragm structure with four sides reinforced by combining rigidity and flexibility, and uses flexible materials to cover the slotted gaps 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 at the resonant frequency of the device 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 structure reinforced on four sides 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.

[0126] In an embodiment of the utility model, the piezoelectric MEMS sound-generating unit and the speaker perform electroacoustic conversion through a piezoelectric composite unit. An electrical signal is applied to the piezoelectric composite unit, 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 square, circular, hexagonal and other structures, and is therefore more effective. The modes excited by the rectangular structure reinforced on all four sides 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.

[0127] The present invention also provides a method for preparing a piezoelectric MEMS sound generating unit. Fig.16 As shown, the method comprises the following steps:

[0128] Step S1601, thermally grow an insulating layer on the upper surface and the lower surface of a preset substrate respectively;

[0129] The above-mentioned preset substrate can be an 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 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 thickness of the insulating layer is between 0.1 and 30 um, and can be an insulating material such as silicon nitride, silicon carbide, aluminum nitride, etc., such as 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.

[0130] Step S1602, depositing a seed layer, a bottom electrode layer, and an intermediate layer in sequence from bottom to top on the insulating layer on the upper surface of the substrate to obtain a first structural member; 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;

[0131] The seed layer is conducive to the high-quality growth of the piezoelectric layer; the material of the bottom electrode can 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 lanthanum nickel oxide (LNO), SRO, or composite metal layers, such as: gold / chromium composite layer. Preferably, the thickness of the Pt electrode is between 0.05μm and 3μm, and the thickness of Pt in this case is 0.15μm, etc.

[0132] Grow the bottom piezoelectric layer, the middle electrode layer, and the top piezoelectric layer. For example, the two piezoelectric layers of the piezoelectric MEMS generating unit D10 are single crystal PZT thin films, each with a thickness of 1.5 μm, and the middle electrode layer and the top electrode layer are Pt, each with a thickness of 0.15 μm. Fig.18 A cross-sectional schematic diagram after the bottom electrode layer is grown is shown in FIG. Fig.19 A schematic cross-sectional view of a growth intermediate layer is shown. Fig.19 The middle layer in the figure is illustrated by taking two piezoelectric layers as an example.

[0133] Step S1603, patterning the bottom electrode layer and the middle layer in the first structural member to form a first piezoelectric composite unit in each peripheral area of ​​the upper surface of the substrate, thereby obtaining a second structural member after patterning;

[0134] First, the top PZT piezoelectric layer is wet-etched, and then the top PZT piezoelectric layer and the middle electrode layer are dry-etched using IBE (Ion Beam Etching).

[0135] The purpose of wet etching the top PZT piezoelectric layer is to obtain the middle electrode area to facilitate the electrical connection between the subsequent electrode layers and the lead-out metal wiring. Using IBE dry etching to simultaneously pattern the top PZT piezoelectric layer and the middle electrode layer is beneficial to avoid etching the top PZT piezoelectric layer and the middle electrode layer in steps, which may cause the PZT film to be over-etched due to different etching selectivities.

[0136] Dry IBE etches the PZT piezoelectric layer and electrode layer. The etching of the PZT piezoelectric film and the electrode layer is at an angle, which is conducive 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 layer and the bottom electrode layer is <30%; the smaller the roughness of the PZT side wall, the better. The goal is that after the passivation layer is deposited, there is no delamination between the sliced ​​PZT and the passivation layer. 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 distance between each layer is less than 3μm. Fig. 20 A schematic cross-sectional view of a patterned top piezoelectric layer and a middle electrode layer is shown; Fig.21 A schematic cross-sectional view of a patterned bottom piezoelectric layer and bottom electrode layer is shown.

[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 structural member to isolate the electrical connection of each electrode layer, and patterning the passivation layer to form a pad area to lead out the bottom electrode layer and the middle electrode layer of each first piezoelectric composite unit to obtain a third structural member;

[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 units 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., and the thickness can be 0.2μm, etc. Fig. 22 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 structural member to form a pad and a top electrode layer, depositing a passivation layer on the top electrode layer, and patterning the passivation layer to obtain a fourth structural member;

[0141] like Fig.23A schematic cross-sectional view of a metal wire after deposition and patterning is shown. In an embodiment, a liftoff 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 units in each area, such as connecting the units in parallel or in series. 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 0.5μm, etc. Fig.23 In the embodiment, the metal layer deposited on the top piezoelectric layer is used as the top electrode layer, and a passivation layer can be deposited on the top electrode layer, such as Fig.24 A schematic cross-sectional view of a passivation layer after deposition and patterning is shown.

[0142] Step S1606, etching the middle rectangular area of ​​the Si layer of the substrate device on the upper surface of the fourth structural member to form a slotted gap, and covering the slotted gap with a flexible material to obtain a fifth structural member;

[0143] like Fig.25 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. The shape of the groove obtained by etching is: inner and outer rings, and long slots, but it can also be an etched area layer of other shapes, including square, rectangular or polygonal, 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 15μm-2000μm, etc. Fig.26 The schematic cross-sectional view of a structure coated with a flexible film material is shown, wherein the slotted gap is covered with the flexible film material.

[0144] Step S1607, performing a thinning process and a cavity etching process on the bottom surface of the substrate of the fifth structural component to obtain a piezoelectric MEMS sound generating unit; wherein the cavity obtained by etching is located in the bottom center area of ​​the substrate.

[0145] In this embodiment, wafer thinning CMP (Chemical-Mechanical Planarization) to 300 μm is conducive to thinning the device thickness, and double-sided exposure technology DRIE is used to etch the back cavity and the BOX layer of SOI, thereby obtaining 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 width size change. 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 piezoelectric MEMS sound unit can reduce the internal stress of each membrane layer in the diaphragm structure of the piezoelectric MEMS sound unit caused by the process by setting slots and gaps; using flexible materials to cover the slots and gaps can improve the flexibility of the diaphragm structure, while reducing the sound leakage of the piezoelectric MEMS sound unit at low frequencies, increasing the vibration amplitude and the emission sound pressure level, and using low-density flexible materials to replace the high-density silicon diaphragm to reduce the mass of the diaphragm structure, and increase the damping of the diaphragm system through the rigid-flexible diaphragm structure, reduce the vibration quality factor Q value, and thus reduce or reduce resonance within a larger sound frequency range. Reducing the nonlinearity caused by the large diaphragm excursion at the resonant frequency of the device is conducive to improving the sound pressure level SPL frequency response curve and the THD frequency response curve, thereby improving the sound quality of the piezoelectric MEMS sound unit.

[0148] This embodiment mainly improves the following contents: (1) The structural form of the piezoelectric MEMS sound generating unit, such as the rectangular four-sided reinforcement structure, the double-layer piezoelectric composite unit distribution, the different shapes, sizes and positions of the gap, and the different shapes, sizes and positions of the flexible material covering. (2) The device manufacturing process that combines rigidity and flexibility. (3) The polarization mode of the piezoelectric film in the piezoelectric composite unit and the electrical connection method of different piezoelectric composite units, the dual drive electrode with a piston mode of a 180° anti-phase drive structure to improve the emission sound pressure level of the piezoelectric MEMS generating unit. (4) The structure of the speaker array.

[0149] 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 piezoelectric MEMS sound unit, characterized in that: include: substrate; A first piezoelectric composite unit is respectively arranged in each peripheral area of ​​the upper surface of the substrate; The bottom center area of ​​the substrate has a cavity, and at least a portion of each of the first piezoelectric composite units is located in the upper area of ​​the substrate; the upper area is the area corresponding to the orthographic projection of the cavity toward the upper surface of the substrate; In the middle rectangular area of ​​the upper area excluding at least a part of each of the first piezoelectric composite units, a slotted gap is provided, and the slotted gap is covered with a flexible material, and the upper area of ​​the substrate with the flexible material forms a diaphragm structure of the piezoelectric MEMS sound unit; each diaphragm edge of the diaphragm structure is anchored, and a gap structure is provided between the first piezoelectric composite units of each two adjacent peripheral areas.

2. The piezoelectric MEMS sound generating unit according to claim 1, characterized in that: At least one second piezoelectric composite unit is provided in the upper area of ​​the substrate; a slotted gap is provided on each of the second piezoelectric composite units, and / or a slotted gap is provided in the middle rectangular area except for each of the second piezoelectric composite units; the slotted gap is covered with a flexible material.

3. The piezoelectric MEMS sound generating unit according to claim 1 or 2, characterized in that: The slotted gap comprises: at least one slotted structure of a preset shape; If the width of the slotted structure is between 0.5 μm and 5 μm, the preset shape includes at least one of the following: a straight line, a circle, a square or a polygon; If the width of the slotted structure is between 10 μm and 200 μm, the preset shape includes at least one of the following: a circle, a square, a ring or a polygon.

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

5. The piezoelectric MEMS sound generating unit according to claim 4, characterized in that: The thickness of the diaphragm structure ranges from 0.1 μm to 50 μm; as the thickness of the diaphragm structure increases, the value of the first-order resonance frequency increases.

6. The piezoelectric MEMS sound generating unit according to claim 2, characterized in that: Each first piezoelectric composite unit and each second piezoelectric composite unit are electrically isolated by an insulating layer and electrically connected by a metal wire.

7. The piezoelectric MEMS sound generating unit according to claim 2, characterized in that: Each of the first piezoelectric composite units and each of the second piezoelectric composite units 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.

8. The piezoelectric MEMS sound generating unit according to claim 7, characterized in that: The thickness of each piezoelectric layer is in the range of 0.1 μm to 25 μm, the thickness of each electrode layer is in the range of 0.01 μm to 5 μm, the thickness of different piezoelectric layers may be the same or different, and the thickness of different electrode layers may be the same or different.

9. The piezoelectric MEMS sound generating unit according to claim 1, characterized in that: At least one rectangular slot is arranged on each first piezoelectric composite unit.

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

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