MEMS loudspeaker with low-pressure sealing back cavity
By designing a low-pressure sealed chamber in a MEMS loudspeaker, the effects of air damping are reduced, allowing for freer diaphragm movement, improving response speed and reducing distortion, thus achieving miniaturization and performance enhancement of the loudspeaker.
Patent Information
- Application Number
- CN202423284672.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-12-26
- Publication Date
- 2025-12-02
- Estimated Expiration
- 2034-12-26
AI Technical Summary
The air inside the back cavity of a MEMS loudspeaker affects the movement of the diaphragm, resulting in a large device size and hindering miniaturization and performance improvement.
Design a low-pressure sealed back cavity MEMS loudspeaker by sealing the cavity on the supporting substrate with a diaphragm to form a low-pressure sealed chamber below standard atmospheric pressure, thereby reducing the influence of air damping on the diaphragm movement.
The diaphragm can vibrate more freely, resulting in a faster response, lower distortion, excellent high-frequency performance, and a smaller overall speaker size.
Smart Images
Figure CN223625998U_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of microelectromechanical systems (MEMS) technology, and more specifically, to a MEMS loudspeaker with a low-pressure sealed back cavity. Background Technology
[0002] With the rapid development of microelectromechanical systems (MEMS) technology, MEMS sound-generating devices such as MEMS loudspeakers, MEMS microphones, and MEMS ultrasonic transducers have shown great application potential in various fields such as consumer electronics, medical diagnostics, and wireless communication. The core of these devices lies in their built-in vibrating thin-film structure, which emits or receives (ultrasonic) waves by precisely controlling its vibration, thus achieving efficient sound conversion and transmission.
[0003] Figure 1 This is a schematic diagram of a traditional piezoelectric MEMS loudspeaker. 11 is the piezoelectric layer, 12 is the support layer, 13 and 14 are connecting lines that connect the device to the PCB, 15 and 16 are the support substrate, typically made of silicon, 17 and 18 are the PCB board, and 19 is the additional back cavity.
[0004] Air inside the back cavity of a MEMS loudspeaker can affect diaphragm movement, so a larger back cavity is usually required, or the cavity should be directly connected to the ambient air to reduce the influence of air. The required back cavity volume of a loudspeaker is related to the mass of the loudspeaker diaphragm, and is typically 200mm. 3 This is much larger than the volume of the MEMS device portion (typically 10mm). 3 (Left and right). This hinders the miniaturization and performance of speakers and electronic devices. Utility Model Content
[0005] To overcome the problem that air inside the back cavity of existing MEMS loudspeakers can affect diaphragm movement, which usually requires a large back cavity or direct connection to the ambient air to reduce the influence of air on the loudspeaker diaphragm and result in a large MEMS loudspeaker size, this utility model provides a MEMS loudspeaker with a low-pressure sealed back cavity.
[0006] The technical solution of this utility model is as follows:
[0007] A MEMS loudspeaker with a low-pressure sealed back cavity, the MEMS loudspeaker comprising:
[0008] A supporting base having a cavity formed thereon;
[0009] A diaphragm is sealed over the supporting substrate to form a low-pressure sealed chamber with a cavity in the supporting substrate. The low-pressure sealed chamber has a pressure lower than standard atmospheric pressure. The diaphragm is provided with electrically drivable electrodes and / or functional materials.
[0010] According to the above-described scheme of this utility model, the pressure of the low-pressure sealed chamber is a vacuum.
[0011] According to the present invention based on the above scheme, a circuit board is provided on the side of the supporting substrate away from the diaphragm, and the electrodes on the diaphragm are connected to the circuit board through connecting wires.
[0012] According to the present invention based on the above scheme, the diaphragm includes a support layer and a piezoelectric layer. The support layer is disposed on the surface of the support substrate and is sealed and covered on the support substrate. The piezoelectric layer is disposed on the support layer.
[0013] According to the above-described scheme of this utility model, the top and bottom surfaces of the piezoelectric layer are formed with metal conductive layers, and the top and bottom metal conductive layers are respectively connected to the circuit board through the connecting lines.
[0014] According to the above-described scheme of this utility model, the surface of the piezoelectric layer is covered with an insulating layer.
[0015] According to the present invention based on the above scheme, the supporting substrate material is silicon, aluminum, or aluminum nitride.
[0016] According to the above-described scheme of this utility model, the depth of the low-pressure sealed chamber is less than 1 mm.
[0017] According to the above-described scheme of this utility model, the depth of the low-pressure sealed chamber is less than 500 micrometers.
[0018] According to the above-described scheme of this utility model, the depth of the low-pressure sealed chamber is less than 5 micrometers.
[0019] According to the above-described solution, the beneficial effects of this utility model are as follows: the MEMS loudspeaker with a low-pressure sealed back cavity is constructed into a low-pressure sealed chamber after the diaphragm seals and covers the cavity on the support substrate. This reduces the pressure inside the low-pressure sealed chamber to below atmospheric pressure, thereby reducing the influence of air damping on the movement of the loudspeaker diaphragm. The reduction in air damping means that the diaphragm can vibrate more freely, with a faster response speed, lower distortion, and better performance in the high-frequency range. Compared with the traditional solution, no additional back cavity is required, reducing the overall volume of the loudspeaker. Attached Figure Description
[0020] Figure 1 A schematic diagram of the structure of an existing MEMS loudspeaker;
[0021] Figure 2 Top view of the planar structure of this utility model;
[0022] Figure 3 for Figure 2 A side view cut along line AA.
[0023] Figure 4 for Figure 2 A cross-sectional view of the section cut along line AA in the middle;
[0024] Figure 5 The frequency response curves of the MEMS speaker of this invention and existing MEMS speakers are shown.
[0025] In the figure, the various attached figures are labeled as follows:
[0026] 100, Supporting substrate; 101, Cavity; 200, Diaphragm; 203, Supporting layer; 204, Second conductive metal layer; 205, Piezoelectric layer; 206, First conductive metal layer; 300, Circuit board; 400, Connecting wire. Detailed Implementation
[0027] To make the technical problems, technical solutions and beneficial effects of this utility model clearer, the present utility model will be further described in detail below with reference to the accompanying drawings and embodiments.
[0028] It should be noted that the terms "comprising" and "having," and any variations thereof, in the specification and claims of this utility model are intended to cover non-exclusive inclusion. 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 not listed, or may optionally include other steps or units inherent to these processes, methods, products, or devices. Terms such as "set up" should be interpreted broadly; for example, it can refer to a fixed connection, a detachable connection, or an integral part; it can refer to a mechanical connection or an electrical connection; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication of two elements or the interaction between two elements, unless otherwise expressly defined. Terms such as "upper," "lower," "left," "right," "front," "rear," and "bottom" indicate orientations or positions based on the orientations or positions shown in the accompanying drawings, and are only for ease of description and should not be construed as limiting the present technical solution.
[0029] It should be noted that, as Figure 1 As shown, Figure 1 This is a schematic diagram of a traditional piezoelectric MEMS loudspeaker. 11 is the piezoelectric layer, 12 is the support layer, 13 and 14 are connecting lines that connect the device to the PCB, 15 and 16 are the support substrate, typically made of silicon, 17 and 18 are the PCB board, and 19 is the additional back cavity (the additional back cavity can be part of the loudspeaker package, or it can be implemented through the casing of headphones or mobile phones).
[0030] Air inside the back cavity of a MEMS loudspeaker can affect diaphragm movement, so a larger back cavity is usually required, or the cavity should be directly connected to the ambient air to reduce the influence of air. The required back cavity volume of a loudspeaker is related to the mass of the loudspeaker diaphragm, and is typically 200mm. 3 This is much larger than the volume of the MEMS device portion (typically 10mm). 3 (Left and right). The back cavity often occupies a large space, which is not conducive to the miniaturization and performance of speakers and electronic devices.
[0031] like Figures 2-5 As shown, this embodiment provides a MEMS loudspeaker with a low-pressure sealed back cavity. After the diaphragm 200 seals and covers the cavity 101 on the support substrate 100, it is constructed to form a low-pressure sealed chamber, reducing the pressure inside the low-pressure sealed chamber to below atmospheric pressure. This reduces the influence of air damping on the movement of the loudspeaker 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 range. Compared with traditional solutions, no additional back cavity is required, reducing the overall size of the loudspeaker.
[0032] Specifically, a MEMS loudspeaker with a low-pressure sealed back cavity includes a support substrate 100 and a diaphragm 200, wherein a cavity 101 is formed on the support substrate 100; the diaphragm 200 is sealed and covered on the support substrate 100 so that the cavity 101 formed on the support substrate 100 forms a low-pressure sealed chamber, the low-pressure sealed chamber has a pressure lower than standard atmospheric pressure, and the diaphragm 200 is provided with electrically drivable electrodes and / or functional materials (such as piezoelectric films, electromagnetic films).
[0033] When no sound reaches the diaphragm 200, the diaphragm 200 can assume a corresponding static position or configuration. Depending on the density in the low-pressure sealed chamber, lower pressure results in weaker damping. Simultaneously, the diaphragm, which withstands normal pressure and senses sound, may not require any back cavity volume because there may be very small forces or no forces transferred to the electrodes on the diaphragm 200 via fluid coupling. To give some figures, the diaphragm may have to withstand absolute pressures up to approximately 100 kPa. The sensed sound pressure could, for example, be in the range of up to approximately 1 MPa or up to 10 MPa.
[0034] Figure 5 The figures show the frequency response curves of the MEMS loudspeaker and the conventional loudspeaker in this embodiment. It is clear from the figures that the smaller the back cavity of the conventional piezoelectric MEMS loudspeaker, the higher the resonant frequency and the lower the sound pressure level. Compared to the conventional piezoelectric MEMS loudspeaker, the piezoelectric MEMS loudspeaker with a low-pressure sealed cavity achieves a 5dB higher sound pressure level at the same resonant frequency, and requires no additional back cavity, thus reducing the loudspeaker size.
[0035] In one embodiment, the pressure of the low-pressure sealed chamber is a vacuum or near-vacuum. In other instances of implementation, 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 is typically 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 any case, the pressure of the low-pressure sealed chamber may typically be selected as a range that is below standard atmospheric pressure, which is appropriate for the weather conditions that should be reasonably expected for the MEMS microphone to be used and relative to altitude (e.g., up to 9000 meters above sea level).
[0036] In one embodiment, a circuit board 300 is provided on the side of the support substrate 100 away from the diaphragm 200, and electrodes on the diaphragm 200 are connected to the circuit board 300 via connecting lines 400. The circuit board 300 is responsible for receiving audio signals and transmitting them to the electrodes. When the audio signal passes through the electrodes, it generates a changing electric or magnetic field, which in turn drives the diaphragm 200 to vibrate according to the waveform of the audio signal. This vibration then pushes the surrounding air molecules, generating sound waves, which are the sounds we hear.
[0037] The diaphragm 200 includes a support layer 203 and a piezoelectric layer 205. The support layer 203 is deposited on the surface of the support substrate 100 and seals over the cavity 101 of the support substrate 100, thereby forming a low-pressure sealed chamber. The piezoelectric layer 205 is deposited on the support layer 203 and deforms when subjected to an electric field, thereby generating sound. To improve the conversion efficiency and stability of the piezoelectric layer 205, conductive metal layers are deposited on both the top and bottom surfaces of the piezoelectric layer 205 to form an electrode structure. The top and bottom conductive metal layers are connected to the circuit board 300 via connecting lines 400, realizing the input and output of audio signals.
[0038] To prevent short circuits between the top and bottom metal conductive layers and to protect the electrodes and connecting wires 400 from external environmental influences, an insulating layer is wrapped around 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.
[0039] The specific process flow is as follows: a cavity 101 is formed on the support substrate 100 and a support layer 203 is bonded thereon; a second metal conductive layer 204 is deposited on the surface of the support layer 203 and etched to form a bottom electrode structure; a piezoelectric layer 205 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 via connecting lines 400. Finally, the entire MEMS speaker is packaged to protect the internal structure and circuit system from the influence of the external environment. This requires depositing insulating materials (such as silicon dioxide, silicon nitride, etc.) on the surfaces of the piezoelectric layer 205 and the metal conductive layer to protect the electrodes and connecting lines 400.
[0040] In one embodiment, the support substrate 100 can be made of metals such as silicon and aluminum, or dielectric materials such as aluminum nitride. Silicon is one of the most commonly used materials in MEMS technology due to its good mechanical properties, thermal stability, and chemical stability, as well as its ease of compatibility with integrated circuit processes. Silicon-based MEMS loudspeakers can be fabricated using standard semiconductor processes, facilitating large-scale production. Aluminum substrates offer better heat dissipation. Dielectric materials such as aluminum nitride are attracting attention in MEMS loudspeakers 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, improving the loudspeaker's conversion efficiency.
[0041] 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 influence of air damping on the movement of the diaphragm 200 can be significantly reduced, improving the speaker's response speed and sound quality. Further, the depth of the low-pressure sealed chamber is less than 500 micrometers. Further reducing the chamber depth to below 500 micrometers can further reduce air damping, further improving the speaker's performance. Further, the depth of the low-pressure sealed chamber is less than 5 micrometers. Reducing the depth of the low-pressure sealed chamber to below 5 micrometers, this depth of chamber almost eliminates the influence of air damping on the movement of the diaphragm 200, bringing the speaker's performance close to its theoretical limit.
[0042] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.
[0043] The present utility model patent has been described above with reference to the accompanying drawings. Obviously, the implementation of the present utility model patent is not limited to the above-described manner. Any improvements made by adopting the inventive concept and technical solution of the present utility model patent, or the direct application of the inventive concept and technical solution of the present utility model patent to other occasions without modification, are all within the protection scope of the present utility model.
Claims
1. A MEMS loudspeaker with a low-pressure sealed back cavity, characterized in that, The MEMS speaker includes: A supporting base having a cavity formed thereon; A diaphragm is sealed over the supporting substrate to form a low-pressure sealed chamber with a cavity in the supporting substrate having a pressure lower than standard atmospheric pressure. The diaphragm is provided with electrically drivable electrodes and / or functional materials.
2. A MEMS loudspeaker with a low-pressure sealed back cavity according to claim 1, characterized in that, The pressure in the low-pressure sealed chamber is a vacuum.
3. A MEMS loudspeaker with a low-pressure sealed back cavity according to claim 1 or 2, characterized in that, A circuit board is provided on the side of the support substrate away from the diaphragm, and the electrodes on the diaphragm are connected to the circuit board via connecting wires.
4. A MEMS loudspeaker with a low-pressure sealed back cavity according to claim 3, characterized in that, The diaphragm includes a support layer and a piezoelectric layer. The support layer is disposed on the surface of the support substrate and is sealed over the support substrate. The piezoelectric layer is disposed on the support layer.
5. A MEMS loudspeaker with a low-pressure sealed back cavity according to claim 4, characterized in that, Metal conductive layers are formed on both the top and bottom surfaces of the piezoelectric layer, and the two metal conductive layers are respectively connected to the circuit board through the connecting lines.
6. A MEMS loudspeaker with a low-pressure sealed back cavity according to claim 4 or 5, characterized in that, The surface of the piezoelectric layer is covered with an insulating layer.
7. A MEMS loudspeaker with a low-pressure sealed back cavity according to claim 1, 2, 4 or 5, characterized in that, The supporting substrate is made of silicon, aluminum, or aluminum nitride.
8. A MEMS loudspeaker with a low-pressure sealed back cavity according to claim 1, 2, 4 or 5, characterized in that, The depth of the low-pressure sealed chamber is less than 1 mm.
9. A MEMS loudspeaker with a low-pressure sealed back cavity according to claim 8, characterized in that, The depth of the low-pressure sealed chamber is less than 500 micrometers.
10. A MEMS loudspeaker with a low-pressure sealed back cavity according to claim 9, characterized in that, The depth of the low-pressure sealed chamber is less than 5 micrometers.