Manufacturing method of small-size MEMS loudspeaker and MEMS loudspeaker

Abstract

The invention discloses a small-size MEMS loudspeaker manufacturing method and an MEMS loudspeaker, the MEMS loudspeaker comprises a support substrate and a diaphragm, and the support substrate is provided with a cavity; the vibrating diaphragm covers the supporting substrate in a sealing mode so that a cavity formed in the supporting substrate can form a low-pressure sealing cavity, the low-pressure sealing cavity has the pressure intensity lower than the standard atmospheric pressure, and an electrically-driven electrode and / or a functional material are / is arranged on the vibrating diaphragm. The low-pressure sealed chamber is constructed after the vibrating diaphragm covers the cavity in the supporting substrate in a sealed mode, the pressure intensity in the low-pressure sealed chamber is reduced to be lower than the atmospheric pressure, and therefore the influence of air damping on the movement of the vibrating diaphragm of the loudspeaker is reduced, and reduction of the air damping means that the vibrating diaphragm can vibrate more freely, the response speed is higher, distortion is lower, and the vibration performance of the loudspeaker is improved. Compared with a traditional scheme, the loudspeaker provided by the invention does not need an additional back cavity, and the overall size of the loudspeaker is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-electromechanical systems (MEMS), and more particularly to a method for manufacturing a small-volume MEMS speaker and a MEMS speaker. Background Art

[0002] With the rapid development of micro-electromechanical system (MEMS) technology, MEMS sound-generating devices such as MEMS speakers, MEMS microphones and MEMS ultrasonic transducers have shown great application potential in consumer electronics, medical diagnosis, wireless communications and other fields. The core of these devices lies in their built-in vibrating film structure, which transmits or receives (super) sound waves by precisely controlling its vibration, thus achieving efficient conversion and transmission of sound.

[0003] Figure 1 This is a schematic diagram of a traditional piezoelectric MEMS speaker. 11 is the piezoelectric layer, 12 is the support layer, 13 and 14 are connecting wires that connect the device to the PCB, 15 and 16 are supporting substrates, generally made of silicon materials, 17 and 18 are PCB boards, and 19 is an additional back cavity.

[0004] The air in the back cavity of a MEMS speaker will affect the movement of the diaphragm, so a larger back cavity is usually required, or it is directly connected to the ambient air to reduce the impact of the air. The volume of the back cavity required by the speaker is related to the mass of the speaker diaphragm, and usually 200mm is required. 3 , which is much larger than the volume of the MEMS device part (usually 10mm 3 This hinders the miniaturization and performance of speakers and electronic devices. Summary of the invention

[0005] In order to overcome the problem that the air in the back cavity of the existing MEMS speaker will affect the movement of the diaphragm, a larger back cavity is usually required, or the back cavity is directly connected to the ambient air to reduce the influence of the air on the speaker diaphragm, resulting in the large volume of the MEMS speaker. The present invention provides a small-volume MEMS speaker manufacturing method and a MEMS speaker.

[0006] The technical solution of the present invention is as follows: A method for manufacturing a small-volume MEMS speaker, comprising: S1. Opening a cavity on a supporting substrate and bonding a supporting layer, and maintaining a vacuum or low-pressure environment during the bonding process of the supporting layer; S2, depositing a second metal conductive layer on the surface of the support layer to form a bottom electrode structure; S3, depositing a piezoelectric layer on the surface of the second metal conductive layer to form a piezoelectric layer structure; S4, depositing a first metal conductive layer on the surface of the piezoelectric layer to form a top electrode structure; S5. Connect the bottom electrode and the top electrode on the diaphragm to the contacts on the circuit board through connecting wires.

[0007] According to the present invention of the above-mentioned aspect, an insulating layer is deposited on the surfaces of the piezoelectric layer, the first metal conductive layer, and the second metal conductive layer in S2, S3, and S4.

[0008] A small-volume MEMS speaker, the MEMS speaker comprising: A supporting substrate, wherein a cavity is formed on the supporting substrate; The diaphragm is sealed and covered on the supporting substrate so that the cavity opened on the supporting substrate forms a low-pressure sealed chamber, and the low-pressure sealed chamber has a pressure lower than the standard atmospheric pressure. The diaphragm is provided with electrically drivable electrodes and / or functional materials.

[0009] According to the present invention of the above scheme, the pressure of the low-pressure sealed chamber is vacuum.

[0010] According to the above-mentioned solution of the present invention, a circuit board is provided on the side of the supporting base away from the diaphragm, and the electrodes on the diaphragm are connected to the circuit board via connecting wires.

[0011] According to the present invention of the above scheme, the diaphragm includes a supporting layer and a piezoelectric layer, the supporting layer is arranged on the surface of the supporting substrate and sealed and covered on the supporting substrate, and the piezoelectric layer is arranged on the supporting layer.

[0012] According to the above-mentioned solution of the present invention, metal conductive layers are formed on the top and bottom surfaces of the piezoelectric layer, and the top and bottom metal conductive layers are respectively connected to the circuit board through the connecting wires.

[0013] According to the present invention of the above aspect, the surface of the piezoelectric layer is covered with an insulating layer.

[0014] According to the above-mentioned solution of the present invention, the support substrate is made of silicon material, aluminum material or aluminum nitride material.

[0015] According to the present invention of the above aspect, the depth of the low-pressure sealing chamber is less than 1 mm.

[0016] According to the present invention of the above aspect, the depth of the low-pressure sealed chamber is less than 500 microns.

[0017] According to the present invention of the above aspect, the depth of the low-pressure sealed chamber is less than 5 microns.

[0018] The beneficial effect of the present invention according to the above scheme is that a small-volume MEMS speaker of the present invention, after covering the cavity on the supporting base through the diaphragm sealing, is constructed into a low-pressure sealed chamber, reducing the pressure in the low-pressure sealed chamber to below atmospheric pressure, thereby reducing the influence of air damping on the movement of the speaker diaphragm. The reduction of air damping means that the diaphragm can vibrate more freely, with faster response speed, lower distortion, and better performance in the high frequency band. Compared with traditional solutions, no additional back cavity is required, thereby reducing the overall volume of the speaker. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a structural schematic diagram of an existing MEMS speaker; Figure 2 A top view of the planar structure of the present invention; Figure 3 for Figure 2 Side view taken along line AA; Figure 4 for Figure 2 A partial cross-sectional view taken along line AA; Figure 5 The frequency response curves of the MEMS speaker of the present invention and the existing MEMS speaker; Fig. 6A is a schematic diagram of S1 in the manufacturing method of the present invention; Figure 6B is a schematic diagram of S2 in the manufacturing method of the present invention; Figure 6C is a schematic diagram of S3 in the manufacturing method of the present invention; Fig.6D It is a schematic diagram of S4 in the manufacturing method of the present invention.

[0020] In the drawings, the reference numerals are as follows: 100, supporting substrate; 101, cavity; 200, diaphragm; 203, supporting layer; 204, second metal conductive layer; 205, piezoelectric layer; 206, first metal conductive layer; 300, circuit board; 400, connecting wire. DETAILED DESCRIPTION

[0021] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0022] It should be noted that the terms "including" and "having" and any variations thereof in the specification and claims of the present invention are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units that are inherent to these processes, methods, products or devices. Terms such as "disposed" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral body; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements, unless otherwise clearly defined. The directions or positions indicated by the terms "upper", "lower", "left", "right", "front", "back", "bottom", etc. are based on the directions or positions shown in the drawings, which are only for the convenience of description and cannot be understood as limitations on the present technical solution.

[0023] It should be noted that if Figure 1 As shown, Figure 1 This is a schematic diagram of a traditional piezoelectric MEMS speaker. 11 is the piezoelectric layer, 12 is the support layer, 13 and 14 are connecting wires that connect the device to the PCB, 15 and 16 are supporting substrates, generally made of silicon materials, 17 and 18 are PCB boards, and 19 is an additional back cavity (the additional back cavity can be part of the speaker package, or it can be realized through earphones or mobile phone shells).

[0024] The air in the back cavity of a MEMS speaker will affect the movement of the diaphragm, so a larger back cavity is usually required, or it is directly connected to the ambient air to reduce the impact of the air. The volume of the back cavity required by the speaker is related to the mass of the speaker diaphragm, and usually 200mm is required. 3 , which is much larger than the volume of the MEMS device part (usually 10mm 3 The back cavity often occupies a large space, which is not conducive to the miniaturization and performance of speakers and electronic devices.

[0025] As shown in FIG6 , a method for manufacturing a small-volume MEMS speaker is shown. This method has significant advantages in the manufacture of small-volume MEMS speakers. It not only improves product performance and reliability, but also reduces manufacturing costs, increases design freedom, and makes it easier to integrate and modularize.

[0026] Specifically, the small volume MEMS speaker manufacturing method includes: S1. Preparation of support substrate and cavity and bonding of support layer: First, a support substrate 100 with high stability and good mechanical properties, such as a silicon substrate, is selected.

[0027] The cavity 101 is precisely opened on the supporting substrate 100 by using precision machining or laser etching technology, and the cavity is used to optimize the acoustic performance of the speaker.

[0028] Under the condition of maintaining vacuum or low pressure environment, the support layer 203 is bonded to the support substrate 100 by wafer bonding technology. The vacuum or low pressure environment in this step helps to eliminate bubbles at the bonding interface, improve the bonding quality, and ensure that the cavity maintains low pressure or vacuum.

[0029] S2. Bottom electrode structure formation: On the clean surface of the support layer 203, a uniform second metal conductive layer 204 is deposited by physical vapor deposition (PVD) or chemical vapor deposition (CVD) technology. Commonly used metal materials include platinum, titanium, nickel-chromium alloy, etc., which are selected according to specific needs to optimize conductivity and adhesion with subsequent layers.

[0030] After deposition, the second metal conductive layer 204 is patterned by photolithography and etching processes to form a desired bottom electrode structure.

[0031] S3. Piezoelectric layer deposition: On the bottom electrode structure, a layer of high-quality piezoelectric material is deposited by sputtering, sol-gel method or chemical vapor deposition technology to form a piezoelectric layer 205. Commonly used piezoelectric materials include PZT (lead zirconate titanate), AIN (aluminum nitride), etc. These materials can produce significant mechanical deformation under the action of an electric field and are the key to achieving electrical-acoustic conversion.

[0032] The temperature, atmosphere and pressure must be strictly controlled during the deposition process to ensure the crystallization quality and performance of the piezoelectric layer.

[0033] S4. Formation of top electrode structure: On the surface of the piezoelectric layer 205, a uniform first metal conductive layer 206 is also deposited by PVD or CVD technology as the top electrode. The material is similar to that of the bottom electrode, and conductivity and adhesion need to be considered.

[0034] The first metal conductive layer 206 is patterned by photolithography and etching processes to form a top electrode structure corresponding to the bottom electrode.

[0035] Additional step: Insulation layer deposition (after S2, S3 and S4, after each layer is deposited): In order to ensure electrical isolation between electrodes and prevent short circuit, a thin insulating layer needs to be deposited on the surface of the second metal conductive layer 204, the piezoelectric layer 205 and the first metal conductive layer 206. The insulating layer material can be silicon dioxide, silicon nitride, etc., and is precisely controlled by CVD or ALD (atomic layer deposition) technology to protect the electrodes and the connecting wires 400.

[0036] The deposition and patterning of the insulating layer must retain the necessary electrode connection points to ensure the effective transmission of electrical signals.

[0037] S5. Electrode connection and packaging: Using precise microelectronic assembly technology, such as gold wire ball welding or conductive adhesive connection, the bottom electrode and the top electrode on the diaphragm 200 are reliably connected to the contacts on the circuit board through connecting wires (such as gold wires).

[0038] Finally, the entire structure is encapsulated to protect the internal components from the external environment while ensuring the effective output of the sound waves. The encapsulation material needs to have good sealing and acoustic transparency. like Figure 2 -As shown in FIG6 , this embodiment provides a small-volume MEMS speaker, which forms a low-pressure sealed chamber by sealing the cavity 101 on the supporting substrate 100 with the diaphragm 200, reducing the pressure in the low-pressure sealed chamber to below atmospheric pressure, thereby reducing the effect of air damping on the movement of the speaker diaphragm 200. The reduction in air damping means that the diaphragm 200 can vibrate more freely, with a faster response speed, lower distortion, and better performance in the high-frequency band. Compared with traditional solutions, no additional back cavity is required, thereby reducing the overall volume of the speaker.

[0039] Specifically, a MEMS speaker with a low-pressure sealed back cavity comprises: a supporting substrate 100 and a diaphragm 200, wherein the supporting substrate 100 is provided with a cavity 101; the diaphragm 200 is sealed and covered on the supporting substrate 100, so that the cavity 101 opened on the supporting substrate 100 forms a low-pressure sealed chamber, the low-pressure sealed chamber has a pressure lower than the standard atmospheric pressure, and the diaphragm 200 is provided with electrically drivable electrodes and / or functional materials (such as piezoelectric film, electromagnetic film).

[0040] When no sound reaches the diaphragm 200, the diaphragm 200 may assume a corresponding rest position or configuration. Depending on the density in the low-pressure sealed chamber, lower pressures may result in weaker damping. At the same time, the membrane that withstands normal pressure and senses sound may not require any back volume, since there may be little or no force transferred to the electrodes on the diaphragm 200 via fluid coupling. To give some numbers as an example, the membrane may have to withstand an absolute pressure of up to about 100 kPa. The sound pressure to be sensed may, for example, be in a range of up to about 1 MPa or up to 10 MPa.

[0041] Figure 5The frequency response curves of the MEMS speaker and the traditional speaker in this embodiment are shown in the figure. It can be clearly seen from the figure that the smaller the back cavity of the traditional piezoelectric MEMS speaker is, the higher the resonant frequency is and the lower the sound pressure level is. Compared with the traditional piezoelectric MEMS speaker, the piezoelectric MEMS speaker with a low-pressure sealed chamber has a 5dB higher sound pressure level under the same resonant frequency condition, and does not require an additional back cavity, which reduces the volume of the speaker.

[0042] In one embodiment, the pressure of the low-pressure sealed chamber is a vacuum or a near-vacuum. In other examples of implementations, the pressure in the low-pressure sealed chamber may be less than about 50% of standard atmospheric pressure. It is also possible that the pressure in the low-pressure sealed chamber may be less than about 45%, 40%, 35%, 30%, 25%, or 20% of standard atmospheric pressure (standard atmospheric pressure may typically be 101.325 kPa or 1013.25 mbar). The pressure in the low-pressure sealed chamber may also be expressed as an absolute pressure, such as less than 50 kPa, less than 40 kPa, less than 30 kPa, or less than 25 kPa. In either case, the pressure of the low-pressure sealed chamber may be generally selected to be a typical range in which it may be lower than standard atmospheric pressure, which is used for meteorological conditions that should be reasonably expected and altitude relative to altitude (e.g., up to 9,000 meters above sea level) in which the MEMS microphone may be used.

[0043] In one embodiment, a circuit board 300 is provided on one side of the supporting substrate 100 away from the diaphragm 200, and the electrodes on the diaphragm 200 are connected to the circuit board 300 via connecting wires 400. The circuit board 300 is responsible for receiving the audio signal and transmitting it to the electrodes. When the audio signal passes through the electrodes, a changing electric field or magnetic field is generated, thereby driving the diaphragm 200 to vibrate according to the waveform of the audio signal. This vibration then pushes the surrounding air molecules to generate sound waves, which is the sound we hear.

[0044] The diaphragm 200 includes a supporting layer 203 and a piezoelectric layer 205. The supporting layer 203 is deposited on the surface of the supporting substrate 100 and sealed on the cavity 101 of the supporting substrate 100, thereby forming a low-pressure sealed chamber. The piezoelectric layer 205 is deposited on the supporting layer 203. When subjected to an electric field, it deforms to produce sound. In order to improve the conversion efficiency and stability of the piezoelectric layer 205, metal conductive layers are deposited on the top and bottom surfaces of the piezoelectric layer 205 to form an electrode structure. The top and bottom two layers of metal conductive layers are connected to the circuit board 300 through connecting wires 400, respectively, to realize the input and output of audio signals.

[0045] In order to prevent short circuit between the top and bottom metal conductive layers and protect the electrodes and connecting wires 400 from the external environment, an insulating layer is coated on the surface of the piezoelectric layer 205 to ensure the connection and shielding of the top and bottom metal conductive layers on the connecting wires 400.

[0046] The specific process flow is as follows: a cavity 101 is opened on the supporting substrate 100 and a supporting layer 203 is bonded; a second metal conductive layer 204 material is deposited on the surface of the supporting layer 203 and etched to form a bottom electrode structure; a piezoelectric layer 205 material is deposited on the surface of the second metal conductive layer 204 and etched to form a piezoelectric layer 205 structure; a first metal conductive layer 206 is deposited on the surface of the piezoelectric layer 205 and etched to form a top electrode structure; the electrodes on the diaphragm 200 are connected to the contacts on the circuit board 300 through connecting wires 400. Finally, the entire MEMS speaker is packaged to protect the internal structure and circuit system from the external environment. Among them, it is necessary to deposit an insulating layer material (such as silicon dioxide, silicon nitride, etc.) on the surface of the piezoelectric layer 205 and the metal conductive layer.

[0047] In one embodiment, the material of the support substrate 100 can be metal such as silicon, aluminum, or dielectric materials such as aluminum nitride. Silicon is one of the most commonly used materials in MEMS technology because it has good mechanical properties, thermal stability and chemical stability, and is easily compatible with integrated circuit processes. MEMS speakers with silicon substrates can be processed through standard semiconductor processes, which is conducive to large-scale production. Aluminum metal substrates have better heat dissipation properties. Dielectric materials such as aluminum nitride have attracted attention in MEMS speakers due to their piezoelectric properties. When these materials are used as the support substrate 100, they not only provide the necessary mechanical support, but also directly participate in the sound generation process, thereby improving the conversion efficiency of the speaker.

[0048] In one embodiment, the depth of the low-pressure sealed chamber is less than 1 mm. When the depth of the low-pressure sealed chamber is set below 1 mm, the effect of air damping on the movement of the diaphragm 200 can be significantly reduced, thereby improving the response speed and sound quality of the speaker. Further, the depth of the low-pressure sealed chamber is less than 500 microns. Further reducing the depth of the chamber to below 500 microns can further reduce air damping, thereby further improving the performance of the speaker. Further, the depth of the low-pressure sealed chamber is less than 5 microns. By reducing the depth of the low-pressure sealed chamber to below 5 microns, a chamber of this depth can almost eliminate the effect of air damping on the movement of the diaphragm 200, bringing the performance of the speaker close to the theoretical limit.

[0049] It should be understood that those skilled in the art can make improvements or changes based on the above description, and all these improvements and changes should fall within the scope of protection of the appended claims of the present invention.

[0050] The above is an exemplary description of the present invention in conjunction with the accompanying drawings. It is obvious that the implementation of the present invention is not limited to the above-mentioned method. As long as various improvements are made by adopting the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A method for manufacturing a small-volume MEMS speaker, characterized in that: include: S1. Preparation of support substrate and cavity and bonding of support layer: opening a cavity on the support substrate and bonding the support layer, and maintaining a vacuum or low-pressure environment during the bonding of the support layer; S2, forming a bottom electrode structure: depositing a second metal conductive layer on the surface of the support layer to form a bottom electrode structure; S3, piezoelectric layer deposition: depositing a piezoelectric layer on the surface of the second metal conductive layer to form a piezoelectric layer structure; S4, forming a top electrode structure: depositing a first metal conductive layer on the surface of the piezoelectric layer to form a top electrode structure; S5. Electrode connection: Connect the bottom electrode and the top electrode on the diaphragm to the contacts on the circuit board through connecting wires.

2. A method for manufacturing a small-volume MEMS speaker according to claim 1, characterized in that: An insulating layer is deposited on the surfaces of the piezoelectric layer, the first metal conductive layer and the second metal conductive layer in S2, S3 and S4.

3. A small-volume MEMS speaker, characterized in that: The small volume MEMS speaker manufactured by the small volume MEMS speaker manufacturing method according to any one of claims 1 or 2 comprises: A supporting substrate, wherein a cavity is formed on the supporting substrate; The diaphragm is sealed and covered on the supporting substrate so that the cavity opened on the supporting substrate forms a low-pressure sealed chamber, and the low-pressure sealed chamber has a pressure lower than the standard atmospheric pressure. The diaphragm is provided with electrically drivable electrodes and / or functional materials.

4. The small-volume MEMS speaker according to claim 3, characterized in that: The pressure of the low-pressure sealed chamber is vacuum.

5. The small-volume MEMS speaker according to claim 4, characterized in that: A circuit board is provided on a side of the support substrate away from the diaphragm, and the electrodes on the diaphragm are connected to the circuit board via connecting wires.

6. The small-volume MEMS speaker according to claim 5, characterized in that: The diaphragm comprises a supporting layer and a piezoelectric layer. The supporting layer is arranged on the surface of the supporting substrate and is sealed and covered on the supporting substrate. The piezoelectric layer is arranged on the supporting layer.

7. The small-volume MEMS speaker according to claim 6, characterized in that: Metal conductive layers are formed on the top and bottom surfaces of the piezoelectric layer, and the top and bottom metal conductive layers are respectively connected to the circuit board through the connecting wires.

8. A small-volume MEMS speaker according to claim 6 or 7, characterized in that: The surface of the piezoelectric layer is covered with an insulating layer.

9. A small-volume MEMS speaker according to claim 3, 4, 6 or 7, characterized in that: The support substrate is made of silicon material, aluminum material or aluminum nitride material.

10. A small-volume MEMS speaker according to claim 3, 4, 6 or 7, characterized in that: The depth of the low pressure sealing chamber is less than 1 mm.

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