MEMS piezoelectric actuator and loudspeaker

Abstract

The utility model relates to the technical field of MEMS loudspeakers, in particular to an MEMS piezoelectric actuator and a loudspeaker, and the MEMS piezoelectric actuator comprises a substrate; the vibrating diaphragm unit is arranged on the substrate, and the edge of the vibrating diaphragm unit is fixedly connected with the substrate; the vibrating diaphragm unit is provided with a spring structure; the piezoelectric composite layer unit is arranged on the vibrating diaphragm unit; and one end of the mass block is connected with the spring structure. According to the MEMS piezoelectric actuator provided by the invention, the vibrating diaphragm unit is provided with the flexible spring structure, so that the vibration amplitude of the MEMS piezoelectric actuator under the excitation of the vibrating diaphragm is improved, and therefore, under the small-size MEMS piezoelectric actuator structure, the sound generating diaphragm with a relatively large effective area is adopted, and the emission sound pressure level under the excitation of the vibrating diaphragm is improved. Besides, the flexibility of the spring of the MEMS piezoelectric actuator and the damping of a vibration system can be increased, so that the risk that the structure of the spring is damaged in the falling and vibration testing process of the device is reduced, and the use reliability is improved.

Description

Technical Field

[0001] This application relates to the technical field of MEMS speakers, and in particular to a MEMS piezoelectric actuator and a speaker. Background Art

[0002] In recent years, piezoelectric MEMS speakers have become a research hotspot. Compared with traditional micro speakers, piezoelectric MEMS speakers do not have the springs and suspensions of the speakers with coils and can be manufactured through reliable semiconductor MEMS processing technologies. Piezoelectric MEMS speakers have the advantages of fast mechanical response, low power consumption, mass production, resistance to reflow soldering, integration with other electronic devices, and low cost. In terms of sound quality, compared with coil speakers, the high-frequency response is improved. Therefore, piezoelectric MEMS speakers have greater advantages in achieving mass-produced miniature high performance.

[0003] In order to make MEMS speakers, such as MEMS microphones, more widely used, the industry is committed to designing small-sized and high-performance MEMS speakers. However, it is often difficult to balance small size and high performance in devices composed of a silicon substrate and piezoelectric thin film materials. For example, in the application of micro speakers, when the MEMS device is small, the effective driving diaphragm area is small, and it is difficult to output a large sound pressure level (SPL). For piezoelectric MEMS speakers with a MEMS actuator and a sound-generating diaphragm structure, the MEMS actuator usually reduces the influence of residual stress in the film layer caused by the process through slit decoupling or partial decoupling. Therefore, how to increase the driving stroke of the MEMS actuator, increase the SPL emitted under the excitation of the MEMS speaker, and how to solve the warping of the MEMS actuator caused by residual stress during the manufacturing process and ensure the reliability of the packaging of the MEMS actuator and the sound-generating diaphragm are problems that need to be solved currently.

[0004] In related technologies, the diaphragm unit expands and contracts in the axial direction of the carrier substrate, and silicon or other compounds are used as the spring structure, which may cause damage to the spring structure during device drop and vibration tests, and the offset amount generated by the actuator under driving is small, resulting in a low output SPL. Summary of the Utility Model

[0005] In view of this, the purpose of the present utility model is to provide a MEMS piezoelectric actuator and a speaker.

[0006] In a first aspect, an embodiment of the present application provides a MEMS piezoelectric actuator, and the MEMS piezoelectric actuator includes:

[0007] A substrate;

[0008] A diaphragm unit, disposed on the substrate, with the edge of the diaphragm unit fixedly connected to the substrate; the diaphragm unit has a spring structure;

[0009] A piezoelectric composite layer unit is provided on the diaphragm unit;

[0010] A mass block, one end of which is connected to the spring structure, and the other end is used to be connected to the sound-emitting film unit; the moving direction of the mass block is the same as the axial direction of the substrate.

[0011] Combined with the first aspect, the diaphragm unit includes two rigid films arranged in sequence and a flexible film located between the two rigid films; a slot is formed on the diaphragm unit to form a spring structure at the center of the diaphragm unit.

[0012] Combined with the first aspect, the mass block is arranged in the cavity below the diaphragm unit; the top end of the mass block is connected to the spring structure, and the bottom end is fixedly connected to the sound-emitting film unit.

[0013] Combined with the first aspect, the mass block is arranged above the diaphragm unit, the bottom end of the mass block is fixedly connected to the spring structure, and the top end is connected to the sound-emitting film unit.

[0014] Combined with the first aspect, the piezoelectric composite layer unit is arranged on the surface of the diaphragm unit away from the mass block.

[0015] Combined with the first aspect, the piezoelectric composite layer unit is arranged on the surface of the diaphragm unit close to the mass block, and the bottom end of the mass block penetrates through the piezoelectric composite layer unit and is fixedly connected to the spring structure.

[0016] Combined with the first aspect, the piezoelectric composite layer unit is a single-layer structure, including an electrode layer at the bottom, a piezoelectric layer, and an electrode layer at the top arranged in sequence from bottom to top.

[0017] Combined with the first aspect, the piezoelectric composite layer unit is a multi-layer structure, including a plurality of electrode layers and piezoelectric layers arranged between adjacent two electrode layers.

[0018] In the second aspect, the present application provides a MEMS piezoelectric loudspeaker, including a sound-emitting film unit and a MEMS piezoelectric actuator as described above, and the sound-emitting film unit is connected to the mass block in the MEMS piezoelectric actuator.

[0019] Combined with the second aspect, the edge of the sound-emitting film is bonded to the edge of the substrate by a dry film or glue.

[0020] The embodiments of the present application bring the following beneficial effects: The MEMS piezoelectric actuator provided by the present application has a flexible spring structure in the diaphragm unit to increase the vibration amplitude of the MEMS piezoelectric actuator under diaphragm excitation. Therefore, with a small-sized MEMS piezoelectric actuator structure, a sounding diaphragm with a relatively large effective area is adopted to increase the emitted sound pressure level under diaphragm excitation. In addition, the flexibility of the spring of the MEMS piezoelectric actuator and the damping of the vibration system can be increased to reduce the risk of damage to the spring structure during the drop and vibration tests of the device and improve the reliability of use.

[0021] Other features and advantages of the present application will be described in the following specification. Moreover, some of them will become apparent from the specification or be understood by implementing the present application. The objectives and other advantages of the present application are achieved and obtained by the structures specifically pointed out in the specification, claims, and drawings.

[0022] To make the above objectives, features, and advantages of the present application more obvious and understandable, the following specific preferred embodiments are given and described in detail in conjunction with the accompanying drawings as follows. Description of the Drawings

[0023] To more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative efforts.

[0024] Figure 1 A top view schematic diagram of the MEMS piezoelectric actuator provided in Embodiment 1 of the present application;

[0025] Figure 2 A three-dimensional cross-sectional schematic diagram of the MEMS piezoelectric actuator provided in Embodiment 1 of the present application;

[0026] Figure 3 A structural schematic diagram of a MEMS piezoelectric speaker provided in Embodiment 1 of the present application;

[0027] Figure 4 A simulation frequency schematic diagram of a MEMS actuator with a silicon spring structure in the related art in Embodiment 1 of the present application;

[0028] Figure 5 A simulation displacement schematic diagram of the diaphragm of a MEMS actuator with a silicon spring structure in the related art in Embodiment 1 of the present application;

[0029] Figure 6 A simulation frequency schematic diagram of the MEMS actuator provided by the present application in Embodiment 1 of the present application;

[0030] Figure 7 This is a schematic diagram of the displacement simulation of the diaphragm unit of the MEMS actuator provided in Embodiment 1 of the present application;

[0031] Figure 8 This is a schematic structural diagram of a MEMS piezoelectric speaker provided in Embodiment 2 of the present application;

[0032] Figure 9 This is a top view schematic diagram of a MEMS piezoelectric speaker provided in Embodiment 3 of the present application;

[0033] Figure 10 This is another schematic structural diagram of a MEMS piezoelectric speaker provided in Embodiment 3 of the present application;

[0034] Figure 11 This is a schematic structural diagram of a MEMS piezoelectric speaker provided in Embodiment 4 of the present application. Detailed implementation manners

[0035] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions of the present application will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0036] It should be noted that the "first", "second", etc. mentioned in the present application are used to distinguish similar objects and do not necessarily need to describe a specific order or sequence. It should be understood that such terms can be interchanged under appropriate circumstances so that the embodiments described here can be implemented in an order different from that shown or described here.

[0037] To facilitate the understanding of this embodiment, the application scenario of the embodiments of the present application will be briefly described below.

[0038] In order to improve the universality of MEMS speakers, the industry is committed to designing MEMS speakers with small size and high performance. However, in the related technologies, no effective solutions have been proposed to improve the driving stroke, reliability of MEMS actuators and the sound pressure level SPL emitted under the excitation of MEMS speakers.

[0039] Embodiment 1

[0040] The present application provides a MEMS piezoelectric actuator, in combination with Figure 1 , Figure 2As shown, the MEMS piezoelectric actuator includes: a substrate 01, a diaphragm unit 60, a piezoelectric composite layer unit (as shown in FIGS. 20a - 20d in the drawing), and a mass block 12. The diaphragm unit 60 is disposed on the substrate 01. The piezoelectric composite layer unit 20a - 20d is provided on the diaphragm unit 60. The diaphragm unit 60 has a spring structure 50. One end of the spring structure 50 is connected to the mass block 12, and the other end of the mass block 12 is used to be connected to a sounding diaphragm unit 18 (not shown in the drawing); wherein, the moving direction of the mass block 12 is the same as the axial direction of the substrate.

[0041] In this application, the diaphragm unit 60 has a spring structure 50, which can reduce the stiffness of the MEMS piezoelectric actuator, increase the vibration amplitude of the actuator under diaphragm excitation and the service reliability, and reduce the risk of structural damage during device drop and vibration tests. In addition, the mass block 12 is connected to the sounding diaphragm unit 18. By adopting a sounding diaphragm unit 18 with a relatively large effective area in the structure of a small - size MEMS piezoelectric actuator, the sound pressure level emitted under diaphragm excitation can be increased, especially the sound pressure level SPL in the low - frequency stage. At the same time, the damping of the piezoelectric MEMS generator system can be increased, the quality factor of device resonance can be reduced, and the total harmonic distortion THD of the device can be reduced. In the drawing, 40b - 40d are the positions of the first cavity 14 below the diaphragm unit 60 shown schematically.

[0042] Combined with the first aspect, combined with Figure 3 、 Figure 4 、 Figure 5 、 Figure 6 As shown, the diaphragm unit 60 includes two rigid thin films (03, 05) arranged in sequence and a flexible thin film 04 located between the two rigid thin films (03, 05); a slotted opening 13 is formed on the diaphragm unit 60 to form a spring structure 50 at the center of the diaphragm unit 60.

[0043] The diaphragm unit 60 provided in this application has a rigid - flexible - rigid sandwich structure, that is, a flexible thin film 04 is further provided between the two rigid thin films (03, 05). Compared with the existing diaphragm unit 60, adopting the rigid - flexible structure in the form of a sandwich can reduce the risk of diaphragm warping or even rupture caused by residual internal stress due to the process. Compared with using silicon or its compounds as the spring structure, adopting a rigid - flexible spring structure can effectively improve the reliability of the device and reduce the risk of spring - structure damage during device drop and vibration tests.

[0044] Among them, the thickness of the diaphragm unit 60 is 0.1 to 100 μm. The material of the rigid thin film constituting the diaphragm unit 60 can be single-crystalline silicon, polycrystalline silicon, or glass; the material of the flexible thin film can be an organic or inorganic compound vibration film, etc. The first resonance frequency of the MEMS piezoelectric actuator is related not only to the stiffness of the diaphragm unit 60 but also to the mass of the diaphragm unit 60. When parameters such as the size of the first cavity 14 are fixed, generally speaking, the thinner the thickness of the diaphragm unit 60, the lower the first resonance frequency. The rear end range of the diaphragm unit 60 is generally between 0.5 μm and 150 μm. After the MEMS piezoelectric actuator device and the size of the first cavity 14 are determined, by changing the diaphragm unit 60 to adjust the resonance frequency, at this time, the lower the thickness of the diaphragm unit, the lower the diaphragm resonance frequency and the lower the stiffness of the MEMS piezoelectric actuator. Then, under the same piezoelectric drive, the deflection displacement generated by the diaphragm unit 60 is larger, the amount of air pushed out is larger, and thus the output sound pressure level is higher.

[0045] The outer edge of the diaphragm unit 60 is anchored to the substrate 01, enabling a firm connection. Slots 13 are formed on the diaphragm unit 60 by means of the DRIE process to form a spring structure 50 at the center of the diaphragm unit 60. The width of the slot 13 is designed between 0.5 μm and 2000 μm, which is used for structural decoupling and simultaneously releases the process internal stress of each film layer, so that a larger driving displacement and sound pressure level output can be obtained. The spring structure 50 is connected to the mass block 12 to form an actuator structure that can move up and down under the action of a driving signal.

[0046] Among them, the thickness of the rigid material of the diaphragm unit 60 is between 0.5 μm and 50 μm, and the width of the slot in the rigid thin film material is between 1 μm and 200 μm. Among them, the shape of the spring structure 50 can be a square, a circle, a ring, a polygon, or other structural shapes. In addition, the flexible material in the diaphragm unit 60 can also be PI, Flexfiner SA, PVI-3, polyurethane, Parylene C, or other organic thin films. The thickness of the flexible material is between 1 μm and 50 μm.

[0047] Combined with the first aspect, the substrate 01 has a first cavity 14 that penetrates along its axis direction.

[0048] Specifically, etching is performed on the back surface of the substrate 01 to form a first cavity 14 that penetrates along the axis direction of the substrate 01. By designing the first cavity 14 structure with different sizes, the resonance frequency of the device can be changed. For the shape of the first cavity 14 of devices such as square, circular, and hexagonal, when the film layer thickness is constant, the larger the size, the lower the first resonance frequency of the device. This size mainly refers to the area of the first cavity 14, but sometimes it can refer to measurement parameters such as length, width, or radius, diameter, etc. The material of the substrate 01 can be silicon, glass, sapphire, etc.

[0049] As an implementable manner, the mass block 12 is disposed in the first cavity 14 of the substrate 01 below the diaphragm unit 60. The top end of the mass block 12 is connected to the spring structure 50, and the bottom end is fixedly connected to the sounding diaphragm unit 18, and the sounding diaphragm unit 18 is fixedly connected to the bottom of the substrate 01, thereby obtaining a MEMS piezoelectric loudspeaker, as shown in combination with Figure 3 and Figure 4 shown.

[0050] As another implementable manner, as shown in combination with Figure 5 and 6 shown, the mass block 12 is disposed above the diaphragm unit 60, the bottom end thereof is connected to the diaphragm unit 60, the top end is connected to the sounding diaphragm unit 18, and the edge of the sounding diaphragm unit 18 is connected to the substrate 01 through the flexible connecting member 17.

[0051] Combined with the first aspect, at least one piezoelectric composite layer unit is provided on the diaphragm unit 60; as an implementable manner, the piezoelectric composite layer unit is disposed on the surface of the diaphragm unit 60 away from the spring structure 50 (as shown in combination with Figure 3 and Figure 5 shown).

[0052] As another implementable manner, the piezoelectric composite layer unit is disposed on the surface of the diaphragm unit 60 close to the mass block 12, and the bottom end of the mass block 12 penetrates through the piezoelectric composite layer unit and is fixedly connected to the spring structure 50 (as shown in combination with Figure 4 and Figure 6 shown).

[0053] Setting at least one piezoelectric layer composite unit on the upper and / or lower surface of the diaphragm unit 60 can cause the diaphragm unit 60 to deform under the drive of an electrical signal, thereby generating sound waves.

[0054] Combined with the first aspect, the piezoelectric composite layer unit is a single-layer structure, including an electrode layer at the bottom, a piezoelectric layer, and an electrode layer at the top, which are sequentially arranged from bottom to top (as shown in combination with Figure 3 and 4 and the reference numeral 06 in FIGS. 5 and 6), a piezoelectric layer (as shown in combination with Figure 3 and 4 and the reference numeral 07 in FIGS. 5 and 6), and an electrode layer at the top (as shown in combination with Figure 3 and 4 and the reference numeral 08 in FIGS. 5 and 6).

[0055] Combined with the first aspect, the piezoelectric composite layer unit is a multi-layer structure, including a plurality of electrode layers and piezoelectric layers disposed between adjacent two electrode layers.

[0056] Among them, the thickness of the piezoelectric layer is 0.1-50 um, and 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.

[0057] The thickness of the electrode layer is 0.05 - 5 μm, and the material can be Mo, Pt, Al, Cu, LNO, and other metal or non-metal conductive films, which can be single-crystal metal materials or alloy materials of the same material.

[0058] Specifically, in combination with Figure 1 , Figure 2 As shown, the substrate 01 has a cavity in the first direction penetrating along its axis direction, the diaphragm unit is arranged above the substrate 01, and the bottom edge of the diaphragm unit is combined with the substrate 01. As shown in Figure 2 As shown, a slit is etched on the diaphragm unit 60 to form a spring structure 50 on the diaphragm unit 60. Since the diaphragm unit 60 is a rigid-flexible-rigid sandwich structure, it has elasticity.

[0059] In combination with Figure 1 As shown, in the top view of the piezoelectric MEMS piezoelectric actuator provided in this application, it includes a diaphragm unit 60 with a rigid-flexible-rigid sandwich structure, and piezoelectric composite units 20a - 20d are arranged on the diaphragm unit 60. Each piezoelectric composite unit is formed into an isosceles trapezoid structure by MEMS etching. Groove-shaped slit structures 30a - 30d etched on the diaphragm unit 60 isolate the units 20a - 20d from each other.

[0060] The middle of the diaphragm unit 60 is a spring structure 50, and the spring structure 50 is connected to the mass block 12. Under the action of the driving electrical signal, the piezoelectric composite units 20a - 20d drive the spring structure 50 on the diaphragm unit 60 to pull the vibration of the mass block 12, and the mass block 12 is connected to the sound-emitting diaphragm unit 1816. When the sound-emitting diaphragm unit 1816 vibrates, sound waves are generated.

[0061] In this embodiment, the spring structure 50 made of a rigid-flexible-rigid sandwich structure thin film has a relatively high tensile strength and a certain elongation rate. Therefore, the MEMS piezoelectric actuator made thereby is not easily broken during the drop and vibration tests, has good reliability, and greatly reduces the probability of damage to the spring structure.

[0062] In combination with Figure 2 As shown, the mass block 12 is located in the cavity and divides the cavity into a first cavity 14 and a second cavity 15.

[0063] As Figure 2 As shown, in this embodiment, the MEMS piezoelectric actuator is a square symmetric structure. The piezoelectric composite layer unit 20c on the upper side of the diaphragm unit 60, and part of the piezoelectric composite units 20b, 20d, and the spring structure 50 are connected to the mass block 12. Under the action of the driving electrical signal, the piezoelectric composite units 20b - 20d drive the spring structure 50 on the diaphragm unit 60 to pull the mass block 12 to vibrate along the axis direction of the substrate.

[0064] Among them, a spring structure 50 is formed by grooving on the diaphragm unit 60 through the DRIE grooving etching MEMS process, releasing the internal stress of the rigid thin film in the diaphragm unit 60 and decoupling the structure at the same time. The use of a flexible thin film and a rigid thin film to form a spring structure 50 reduces the stiffness of the MEMS piezoelectric actuator and increases the vibration amplitude of the actuator under diaphragm excitation. Since the spring structure 50 has a flexible thin film, it can withstand strong drops and impacts and has strong reliability. In addition, the flexible material has a certain elongation rate, and the vibration offset of the MEMS piezoelectric actuator device is larger under the excitation, so that more air volume can be pushed to increase the sound pressure level output.

[0065] In addition, the diaphragm unit 60 combining rigidity and flexibility can reduce the risk of diaphragm warping or even cracking caused by residual internal stress caused by the process. Among them, the selection of the flexible material in the production and manufacturing process needs to meet the following conditions: 1) It needs to be compatible with the MEMS process and can perform processes such as chip bonding, exposure, and etching; 2) It is dustproof, waterproof and insulating, and at the same time meets the bonding of the rigid material plates. Under different humidity conditions, as well as under force or excitation, there will be no phenomena such as film tearing, delamination, and peeling to ensure its use reliability; 3) The flexible material needs to be heat-resistant and can withstand the temperature of the chip bonding and packaging process without causing reliability problems of the device, such as causing the rigid material to crack, etc.; 4) It needs to have a certain elongation rate, and when the device deflects, the flexible material will not be damaged. Based on this, the flexible material in this application is PI, Flexfiner SA, PVI-3, polyurethane, Parylene C, or other organic films, and its thickness should be between 1μm and 50μm.

[0066] In the second aspect, in combination with Figure 3 as shown, this application provides a MEMS piezoelectric speaker, including the above-mentioned MEMS piezoelectric actuator and a sounding diaphragm unit 18.

[0067] In combination with the second aspect, the edge of the sounding diaphragm unit 18 and the edge of the substrate 01 are bonded by a dry film 02 or glue 16.

[0068] In this embodiment, the edge of the sounding diaphragm unit 18 and the edge of the substrate 01 are bonded by a dry film 02 or glue 16, and the middle of the sounding diaphragm unit 18 is tightly connected to the MEMS piezoelectric actuator through a mass block 12, thereby forming the entire MEMS piezoelectric speaker with the MEMS piezoelectric actuator.

[0069] When the MEMS piezoelectric speaker is subjected to a driving voltage signal, the diaphragm unit 60 deforms, driving the connected sounding diaphragm unit 18 to vibrate up and down to generate sound. The driving signal is an electrical signal composed of a DC voltage plus an AC voltage. Generally, the magnitude of the AC voltage does not exceed 30V, and the DC voltage generally does not exceed 15V. The sounding diaphragm unit 18 is a sound film made of materials such as PEEK or PAR, or a sound film made of graphene can also be selected. It has a high elastic modulus, high rigidity, and good absorbability to vibration to ensure high sensitivity.

[0070] In order to improve the rigidity of the bass, a spiral pressure groove is provided above the sounding diaphragm unit 18, which has good damping and can perform perfect piston motion during operation.

[0071] Combined Figure 3 The MEMS piezoelectric speaker shown in

[0072] Above the substrate 01, a diaphragm unit 60 is connected. The diaphragm unit 60 is a sandwich structure composed of a first rigid film 03, a flexible film 04, and a second rigid film 05.

[0073] On the upper side of the diaphragm unit 60, piezoelectric composite layer units 20b, 20d are provided. The piezoelectric composite layer units 20b, 20d can be single piezoelectric layer or multi-piezoelectric layer structures. In this embodiment, each piezoelectric composite layer unit 20b, 20d includes: a bottom electrode layer 06, a piezoelectric layer 07, and an upper electrode layer 08, which can effectively increase the output sound pressure level sensitivity.

[0074] Among them, the surface of the upper electrode layer 08 is a protective layer, and the passivation layer is 09, which plays roles such as electrical insulation and isolation protection. 10 and 11 are metal connection layers or metal welding areas. Metal wires connect the internal and external piezoelectric composite units 20b, 20d of the device, and the metal pad is the connection point of the signal input end.

[0075] On the left side of the piezoelectric composite layer unit 20b and the right side edge of the piezoelectric composite layer unit 20d are anchored to the diaphragm unit 60 of the substrate 01 to be fixedly connected to the diaphragm unit 60. The other side is located above the first cavity 14 or the second cavity 15. Among them, the diaphragm unit 60 is processed by the DRIE process to obtain a gap 13 and a spring structure 50. The width of the gap 13 is designed to be between 0.5um and 2000um, which decouples the structure of the MEMS piezoelectric actuator and releases the process internal stress of each film layer in the diaphragm unit 60, so that a larger driving displacement and sound pressure level output can be obtained. The spring structure 50 is connected to the mass block 12 to form a piezoelectric MEMS actuator structure with the mass block 12 that can move up and down under the action of a driving signal.

[0076] Among them, the mass block 12 in the MEMS piezoelectric speaker is a mass block made of silicon material obtained by deep silicon etching DRIE process, mainly connecting the sounding diaphragm unit 18, used to transmit the force of the piezoelectric MEMS actuator structure and drive the sounding diaphragm unit 18 to move up and down to generate sound.

[0077] In the actual application process, the mass of the mass block 12 has a great influence on the vibration system of the MEMS piezoelectric actuator. On the basis of ensuring reliable connection and driving the movement of the sounding diaphragm unit 18, it is required that the mass of the mass block 12 is as small as possible. This is because in the mid-frequency region of the speaker, the system is controlled by the vibration mass Mms. The larger the Mms, the lower the sound pressure. In this region, the sound pressure is independent of the frequency. Under the same driving force, the smaller the mass, the greater the vibration acceleration, so as to improve the sound pressure level SPL of the mid-high frequency of the speaker.

[0078] Among them, the flexible dry film 02 can be used as an etching mask for the lower surface of the substrate 01 to form the first cavity 14 and the second cavity 15. The sizes of the first cavity 14 and the second cavity 15 affect the resonant frequency and driving offset of the piezoelectric actuator. In the actual MEMS process, due to the difference in process uniformity, there are differences in the cavity sizes in the middle region and the edge region of the wafer, which seriously affects the uniformity of the overall wafer device performance. Through the flexible dry film pressing process, a well-uniform pattern close to a 90-degree vertical wall is formed by etching, and then the first cavity 14 and the second cavity 15 are obtained after the back cavity is etched, which is beneficial to maintaining the consistency of the functional layers above the first cavity 14 and the second cavity 15, and the cavity sizes in the middle region and the edge region of the wafer are relatively consistent, thus facilitating the improvement of the consistency of the MEMS piezoelectric actuator structure and performance of the wafer.

[0079] In this embodiment, the edge of the sounding diaphragm unit 18 is located at the bottom of the substrate 01. The edge of the sounding diaphragm unit 18 is bonded to the bottom of the substrate 01 of the MEMS piezoelectric actuator through the dry film 02 or the glue 16. A flexible connecting member 17 can also be added between the middle part of the sounding diaphragm unit 18 and the mass block 12, so as to form the entire speaker structure with the MEMS piezoelectric actuator.

[0080] In the MEMS piezoelectric speaker, the cavity size, the size of the diaphragm unit 60, and the thickness of the diaphragm unit 60 are closely related to the resonance frequency of the MEMS piezoelectric speaker. The material requirement of the sounding diaphragm unit 18 is that the density is as low as possible to ensure high sensitivity. The MEMS piezoelectric speaker needs to meet the full-band sound generation of 20 Hz to 20 kHz during actual use. On the premise of ensuring that the first resonance frequency (natural frequency) is as low as possible (usually <2 kHz), the MEMS piezoelectric speaker is prone to split vibration at high frequencies, which will reduce the energy use efficiency of the device.

[0081] The material of the sound-emitting diaphragm unit 18 should also have appropriate internal damping to reduce the splitting vibration of the speaker. Currently, commonly used materials include polyarylate (PAR) diaphragms, polyethylene dimethanoate (PEN) diaphragms, polyetheretherketone (PEEK) diaphragms, and polyetherimide (PEI) diaphragms, etc. These materials have extremely high plasticity, are easy to process, and have low costs, but they have poor rigidity, which easily leads to large distortion and difficulty in truly restoring the original sound. It is also possible to choose a sound diaphragm made of graphene, which has a high elastic modulus, high rigidity, and good absorbability for vibration. In this embodiment, the material of the sound-emitting diaphragm unit 18 is a graphene material. In addition, in order to improve the rigidity of the bass of the speaker, spiral pressure grooves are provided on the sound-emitting diaphragm unit 18, which have good damping and can perform perfect piston motion during operation.

[0082] The resonance frequency of the MEMS piezoelectric speaker is related to the stiffness and mass of the diaphragm unit 60. By combining with the diaphragm unit 60 with a flexible material, the elastic coefficient is increased. Since the diaphragm unit 60 has a rigid-flexible-rigid sandwich structure, compared with the existing diaphragm unit 60, the stiffness is reduced. When having the same mass, the low-frequency characteristics of the speaker should be improved. If the diaphragm frequency drops too low, it will affect the high-frequency effect because splitting vibration modes will appear at high frequencies. Therefore, appropriately control the relative area of the flexible material to avoid the resonance frequency being too low.

[0083] The MEMS piezoelectric speaker provided in this embodiment is driven by applying drives to the piezoelectric composite unit 20b, piezoelectric composite unit 20d, etc. Under the action of the drive electrical signal, the piezoelectric composite units 20b, 20d, etc. drive the spring structure 50 on the diaphragm unit 60 to pull the mass block 12 to vibrate, thereby driving the sound-emitting diaphragm unit 18 connected to the mass block 12 to move along the axis direction of the substrate 01, and then pushing the air to emit sound, performing the conversion of mechanical acoustic energy. By setting multiple thin-film piezoelectric membranes, the performance such as the stroke, responsiveness, and durability of the thin-film piezoelectric actuator can be greatly improved.

[0084] Among them, the audio drive signal corresponds to the output acoustic wave signal. The audio drive signal is generally a sine signal with a DC voltage bias DC plus an AC voltage AC. Generally, the magnitude of the AC voltage AC does not exceed 30Vp, and the DC voltage DC generally does not exceed 15V. For example, DV10Vp + AC10V, or it is driven by a bipolar signal. The resonance quality factor Q of a simple piezoelectric MEMS sound-generating device is usually relatively large. After applying excitation, there are spikes and a relatively narrow peak frequency response on its displacement frequency curve or sound pressure level frequency curve. Therefore, the MEMS piezoelectric speaker structure composed of a MEMS piezoelectric actuator and a sound-emitting diaphragm unit 18 can increase the system damping to reduce its resonance Q value, reduce the nonlinearity caused by large diaphragm offset at the device resonance frequency, so that the sound pressure level curve becomes flat, and reduce the total harmonic distortion THD and intermodulation distortion IM.

[0085] Combined Figure 4 、 Figure 5 As shown, the MEMS piezoelectric actuator structure provided by this application can be a bridge structure with the opposite sides reinforced. It can also be a circular, rectangular or polygonal structure with the surrounding sides reinforced. In this embodiment, the MEMS piezoelectric actuator is a square structure with a size of 3mm×3mm. It has a single-layer piezoelectric PZT film structure, and the substrate 01 is an SOI substrate silicon wafer. An excitation voltage of DC: 15V is applied to this MEMS piezoelectric actuator.

[0086] The simulation frequency of the MEMS piezoelectric actuator with a silicon spring structure is as Figure 4 shown, and the diaphragm displacement is as Figure 5 shown; the simulation frequency of the MEMS piezoelectric actuator with the rigid-flexible-rigid sandwich structure diaphragm unit 60 provided by this application is as Figure 6 shown, and the displacement of the diaphragm unit is as Figure 7 shown.

[0087] The piezoelectric MEMS actuator resonance frequency (as Figure 4 shown) and the maximum vibration displacement of the mass block (as Figure 5 shown) of the MEMS actuator with a silicon spring structure in the prior art are obtained through simulation.

[0088] At the same time, the MEMS actuator with a rigid-flexible spring structure in the form of a sandwich is simulated to obtain the piezoelectric MEMS actuator as provided by this application, and the resonance frequency (as Figure 6 shown) and the maximum vibration displacement of the mass block (as Figure 7 shown) of this MEMS piezoelectric actuator are obtained.

[0089] Combined Figures 4 - 7 it can be seen that: the resonance frequency of the device with a silicon spring structure is 8.81kHz, and the maximum displacement of the mass block is 38.9um. While the resonance frequency of the device with a rigid-flexible spring structure in the form of a sandwich is 8.0kHz, and the maximum displacement of the mass block is 48.6um.

[0090] In summary, in the prior art, silicon or its compounds are used for the MEMS diaphragm, and the quality factor Q of resonance is usually relatively large. After applying excitation, there are sharp peaks and narrow peak frequency responses on its displacement frequency curve or sound pressure level frequency curve, thus resulting in total harmonic distortion THD of the device. In addition, the size of the single-chip MEMS loudspeaker that realizes driving and diaphragm in silicon in the prior art is usually relatively large, and the generated sound pressure level is relatively low.

[0091] The MEMS piezoelectric actuator provided by the present application has a reduced resonance frequency of the MEMS piezoelectric actuator with a rigid-flexible spring structure, has good elasticity, and is prone to large-amplitude vibration under the action of electric drive, thereby improving the vibration amplitude and emitted sound pressure level of the MEMS piezoelectric speaker.

[0092] Embodiment 2

[0093] Combined with Figure 8 As shown, another difference feature of the MEMS piezoelectric speaker S02 provided in this embodiment from the MEMS piezoelectric speaker S01 provided by Figure 3 is that the piezoelectric composite layer units 20b and 20d in the MEMS piezoelectric speaker S02 provided in this embodiment are arranged on the lower side of the diaphragm unit. Its working principle is the same as that of the above-mentioned MEMS piezoelectric speaker, and will not be elaborated here.

[0094] Embodiment 3

[0095] Combined with Figure 9 As shown, another MEMS piezoelectric speaker provided in the embodiment of the present application, compared with the MEMS piezoelectric speakers provided in Embodiment 1 and Embodiment 2, in addition to arranging the piezoelectric composite layer units 20a-20d with an isosceles trapezoid structure on the diaphragm unit 60 of the MEMS piezoelectric speaker provided by the present application, a piezoelectric composite layer unit 20e is also provided in the middle area of the diaphragm unit 60 with a rigid-flexible-rigid sandwich structure. The piezoelectric composite layer unit 20e is isolated from the piezoelectric composite layer units 20a-20d, electrically parallels the outer piezoelectric composite layer units 20a-20d on the diaphragm unit 60 of the MEMS piezoelectric actuator, and is electrically connected in series with the inner piezoelectric composite layer unit 20e, which can improve the driving force of the MEMS piezoelectric actuator, so that the MEMS piezoelectric actuator can obtain a larger displacement, force or rotation angle, and thus the speaker can obtain a larger emitted sound pressure level compared with the structure in the prior art.

[0096] Combined with Figure 10 As shown, in another MEMS piezoelectric speaker S03 provided in this embodiment, the sounding diaphragm unit 18 is arranged above the substrate 01, and the edge of the sounding diaphragm unit 18 is bonded to the substrate 01 through a dry film or glue 16. A diaphragm unit 60 (not marked in the figure) is provided on the substrate 01. The diaphragm unit 60 is a diaphragm with a rigid-flexible-rigid sandwich structure composed of 03, 04, and 05. In S03, the mass block 12 is replaced by a flexible connecting member 17, and the connecting member 17 can be a dry film or glue.

[0097] Specifically, the substrate 01 has a first cavity 14. A diaphragm unit 60 is disposed above the substrate 01, and a plurality of piezoelectric composite layer units 20b, 20d, 20e are disposed above the diaphragm unit 60. A slit 13 is formed in the diaphragm unit 60 to form a spring structure 50, and the spring structure 50 is connected to a sounding diaphragm unit 18 through a mass block 12. The sounding diaphragm unit 18 is connected to the spring structure 50 through a flexible connector 17 and is fixedly connected to the substrate 01 through a dry film 02. Its working principle is the same as that of the MEMS piezoelectric speaker provided in Embodiment 1 and Embodiment 2, and will not be elaborated here.

[0098] Embodiment 4

[0099] Combined Figure 11 As shown, another MEMS piezoelectric speaker S04 is provided in an embodiment of the present application. Compared with the MEMS piezoelectric speaker S03 provided in Embodiment 3, the difference is that in the MEMS piezoelectric speaker S04 provided in the present application, the piezoelectric composite layer units 20b, 20d, 20e are disposed below the diaphragm unit 60.

[0100] In this embodiment, the sounding diaphragm unit 18 is located above the substrate 01, and the edge of the sounding diaphragm unit 18 is bonded to the top edge of the substrate through a dry film or glue 16. The middle area of the sounding diaphragm unit 18 is connected to the spring structure 50 through a flexible connector 17, thereby forming the entire speaker structure with the MEMS piezoelectric actuator. Its principle is the same as that of the MEMS piezoelectric speaker in the above embodiment. In the MEMS piezoelectric speakers provided in Embodiment 3 and this embodiment, there is no mass block 12 made of silicon material obtained by the deep silicon etching DRIE process. The left and right ends of the sounding diaphragm unit 18 are mainly connected through a dry film or glue 16, and the middle area of the sounding diaphragm unit 18 is connected through a flexible spring structure 50, which functions to connect the sounding diaphragm unit 18 and transmit the force of the piezoelectric MEMS actuator structure and drive the sounding diaphragm to move up and down to generate sound. Without the silicon mass block 12, the mass of the vibration system of the MEMS piezoelectric speaker is reduced a lot. Under the same driving force, the smaller the mass of the vibrating part of the piezoelectric MEMS speaker, the greater the vibration acceleration of the device, so that the sound pressure level SPL of the mid-high frequency of the speaker can be further improved.

[0101] In addition, in the description of the embodiments of the present application, unless otherwise clearly specified and limited, the terms "mounted", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those skilled in the art, the specific meanings of the above terms in the present application can be understood according to specific situations.

[0102] If a function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a part of this technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods of various embodiments of this application. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs.

[0103] In the description of this application, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, it should not be understood as a limitation to this application. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0104] Finally, it should be noted that: the above embodiments are only specific implementation manners of this application, used to illustrate the technical solutions of this application, rather than limiting it. The protection scope of this application is not limited thereto. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: any person skilled in the art within the technical scope disclosed in this application can still modify the technical solutions recorded in the foregoing embodiments, or can easily think of changes, or perform equivalent replacements on some of the technical features; and these modifications, changes, or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of this application, and should all be covered within the protection scope of this application. Therefore, the protection scope of this application should be subject to the protection scope of the claims.

Claims

1. A MEMS piezoelectric actuator, characterized in that, The MEMS piezoelectric actuator includes: A substrate; A diaphragm unit disposed on the substrate, with the edge of the diaphragm unit fixedly connected to the substrate; the diaphragm unit has a spring structure; A piezoelectric composite layer unit disposed on the diaphragm unit; A mass block, one end of which is connected to the spring structure and the other end is used to connect to a sounding film unit; the moving direction of the mass block is the same as the axis direction of the substrate.

2. The MEMS piezoelectric actuator according to claim 1, wherein, The diaphragm unit includes two rigid thin films arranged in sequence and a flexible thin film located between the two rigid thin films; slotted gaps are formed on the diaphragm unit to form a spring structure at the center of the diaphragm unit.

3. The MEMS piezoelectric actuator according to claim 1, wherein A cavity is formed in the substrate; the mass block is disposed in the cavity below the diaphragm unit; the top end of the mass block is connected to the spring structure, and the bottom end is fixedly connected to the sounding film unit, and the sounding film unit is fixedly connected to the bottom of the substrate.

4. The MEMS piezoelectric actuator according to claim 1, characterized in that, The mass block is disposed above the diaphragm unit, the bottom end of the mass block is fixedly connected to the spring structure, and the top end is connected to the sounding film unit, and the sounding film unit is also fixedly connected to the upper surface of the substrate.

5. The MEMS piezoelectric actuator according to claim 4, characterized in that, The piezoelectric composite layer unit is disposed on a surface of the diaphragm unit away from the mass block.

6. The MEMS piezoelectric actuator according to claim 4, characterized in that The piezoelectric composite layer unit is disposed on a surface of the diaphragm unit close to the mass block, and the bottom end of the mass block penetrates through the piezoelectric composite layer unit and is fixedly connected to the spring structure.

7. The MEMS piezoelectric actuator according to claim 1, wherein The piezoelectric composite layer unit is a single-layer structure, including an electrode layer at the bottom, a piezoelectric layer, and an electrode layer at the top arranged in sequence from bottom to top.

8. The MEMS piezoelectric actuator according to claim 1, characterized in that, The piezoelectric composite layer unit is a multi-layer structure, including a plurality of electrode layers and piezoelectric layers disposed between adjacent two electrode layers.

9. A MEMS piezoelectric speaker, characterized in that, It includes a sounding film and the MEMS piezoelectric actuator according to any one of claims 1-8.

10. The MEMS piezoelectric speaker according to claim 9, wherein, The edge of the sounding film is bonded to the edge of the substrate by a dry film or glue.

Images