A MEMS transducer based on acoustic streaming effect, preparation method and microphone device
By designing a MEMS transducer based on the acoustic flow effect, and utilizing a cantilever beam structure and multilayer composite layered electrodes, the microphone's response to low-frequency sound waves is enhanced, solving the problem of weak low-frequency response in traditional microphones and improving sensitivity and signal-to-noise ratio.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HAINING CHAOTONG NEW POWER SYSTEM TECHNOLOGY RESEARCH INSTITUTE
- Filing Date
- 2026-04-10
- Publication Date
- 2026-07-10
AI Technical Summary
Traditional directional microphones have a weak response to low-frequency sound waves, resulting in insufficient pressure difference to drive the diaphragm, weak vibration amplitude, and low converted electrical signal strength, which affects overall performance.
A MEMS transducer design based on the acoustic flow effect is adopted, which utilizes a cantilever beam structure with movable and fixed electrodes, combined with a multi-layered composite layered structure and surface morphology structure to enhance the acoustic response, especially the low-frequency response performance.
It improves the microphone's sensitivity and signal-to-noise ratio, enhances the driving force for low-frequency sound waves, improves low-frequency response performance, and significantly improves signal strength and signal-to-noise ratio through a dual-capacitor structure.
Smart Images
Figure CN122372915A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of microphone technology, and more specifically, to a MEMS transducer based on acoustic flow effect, its fabrication method, and a microphone device. Background Technology
[0002] Directional microphones are significantly more sensitive to sound waves from a specific direction than to other directions, enabling them to selectively focus on a target sound source and suppress noise from non-target directions. Traditional directional microphones operate based on the principle of sound wave pressure difference: when sound waves are incident from different directions, they arrive at the diaphragm at different times and in different phases, creating a pressure difference that drives the diaphragm to vibrate. Sound waves from non-target directions are suppressed in amplitude due to phase cancellation or a weak pressure difference, thus achieving directional selectivity.
[0003] In a typical capacitive MEMS transducer, a diaphragm is positioned above or below a fixed electrode or backplate, forming a parallel-plate capacitor. When the diaphragm vibrates under a pressure difference, the distance between the diaphragm and the backplate changes, and the capacitance of the device changes accordingly, thus achieving acoustic-to-electrical conversion.
[0004] However, the inventors discovered that traditional directional microphones have the following drawbacks: low-frequency sound waves propagate with slow phase changes, resulting in minimal phase difference when incident on the diaphragm from any direction, causing the pressure difference across the diaphragm to approach zero. The diaphragm lacks sufficient pressure difference to drive it, resulting in weak vibration amplitude, low-intensity converted electrical signals, and ultimately, a weak low-frequency response, affecting the overall performance of the microphone. Summary of the Invention
[0005] The purpose of this invention is to provide a MEMS transducer based on acoustic flow effect, its fabrication method, and a microphone device, which can enhance the response to sound waves, especially improve low-frequency response performance, and increase sensitivity and signal-to-noise ratio.
[0006] The embodiments of the present invention are implemented as follows: In a first aspect, a MEMS transducer based on the acoustic flow effect according to this embodiment includes: A substrate having a front side and a back side; A fixed electrode is disposed on the front side of the substrate. The fixed electrode includes a first cantilever beam, one end of which is fixedly connected to the substrate and the other end is a free end. A first protrusion structure is provided on the side of the first cantilever beam. A movable electrode is disposed on the front side of the substrate and spaced apart from the fixed electrode in a first direction. The movable electrode includes a front diaphragm plate and a second cantilever beam integrally connected. One end of the second cantilever beam is fixedly connected to the substrate. The surface of the front diaphragm plate is provided with a plurality of surface structures that do not penetrate its thickness. The side of the second cantilever beam is provided with a second protrusion structure. The second protrusion structure and the first protrusion structure are arranged alternately in the first direction. The movable electrode is capable of vibrating relative to the fixed electrode in a second direction to change the capacitance value between the movable electrode and the fixed electrode. A back cavity is formed on the back side of the substrate, and the projection area of the back cavity on the front side of the substrate covers the mounting areas of the movable electrode and the fixed electrode.
[0007] In a possible implementation, both the movable electrode and the fixed electrode are multilayer composite layered structures, which are formed by alternating stacks of insulating and conductive layers. In a possible implementation, the surface structure is a raised structure or a recessed structure, and the surface structure is arranged in an array; the first raised structure and the second raised structure are both strip-shaped raised structures, and the strip-shaped raised structures are arranged along the extension direction of the cantilever beam. In a possible implementation, the back cavity is a groove structure formed by a deep silicon etching process, and the depth of the back cavity is 1 / 2 to 4 / 5 of the thickness of the substrate. Secondly, a MEMS transducer based on the acoustic flow effect in this embodiment includes: A substrate having a front side and a back side; A movable electrode is disposed on the front side of the substrate and includes an integrally connected front diaphragm plate and a cantilever beam. One end of the cantilever beam is fixedly connected to the front side of the substrate. The surface of the front diaphragm plate is provided with multiple surface structures that do not penetrate its thickness. An upper fixed electrode back plate is provided, which is disposed on one side of the cantilever beam of the movable electrode and is fixedly connected to the substrate. A lower fixed electrode back plate is provided, which is disposed on the other side of the cantilever beam of the movable electrode and is fixedly connected to the substrate. A first cavity is formed between the movable electrode and the upper fixed electrode back plate, and a second cavity is formed between the movable electrode and the lower fixed electrode back plate. The first cavity and the second cavity are interconnected. The movable electrode can vibrate in the second direction to simultaneously change the first capacitance value between the movable electrode and the upper fixed electrode back plate, and the second capacitance value between the movable electrode and the lower fixed electrode back plate. A back cavity is formed on the back side of the substrate, and the projection area of the back cavity on the front side of the substrate covers the mounting area of the movable electrode. In a possible implementation, both the upper fixed electrode backplate and the lower fixed electrode backplate are multi-layered composite layered structures, which are formed by alternating stacking of insulating and conductive layers; the first cavity and the second cavity are interconnected by a connecting channel, the width of which is smaller than the width of the cantilever beam of the movable electrode.
[0008] Thirdly, a fabrication method of this embodiment, applied to the above-mentioned MEMS transducer based on acoustic flow effect, includes the following steps: Step S1: Provide a substrate; Step S2: Sequentially deposit a first insulating layer, a conductive layer, and a second insulating layer on the front side of the substrate, and perform patterning processing on the first insulating layer, the conductive layer, and the second insulating layer to form the basic outline of the movable electrode and the fixed electrode. Step S3: Form a conductive metal layer on the surface of the patterned layered structure; Step S4: Using an etching process, multiple non-penetrating surface structures are etched in the diaphragm plate area at the front end of the movable electrode, and a gap is etched between the movable electrode and the fixed electrode, so that the side protrusion structures of the two are arranged in an alternating pattern. Step S5: Etch the back side of the substrate to form a back cavity corresponding to the mounting areas of the movable electrode and the fixed electrode.
[0009] In a possible implementation, in step S2, the deposition process is chemical vapor deposition or physical vapor deposition; in step S3, the process for forming the metal conductive layer is sputtering; in step S4, the depth of etching the surface structure is 1 / 3 to 2 / 3 of the overall thickness of the front-end diaphragm plate; in step S5, the depth of the back cavity is 1 / 2 to 4 / 5 of the substrate thickness.
[0010] Fourthly, a fabrication method of this embodiment, applied to the above-mentioned MEMS transducer, includes: Step S1: Provide a substrate; Step S2: Sequentially deposit a first insulating layer, a conductive layer, and a second insulating layer on the front side of the substrate, and perform patterning processing on the first insulating layer, the conductive layer, and the second insulating layer to form the basic outline of the movable electrode and the fixed electrode. Step S3: A lower fixed electrode backplate is formed at a predetermined position on the front side of the substrate, and a first sacrificial layer is formed on the surface of the lower fixed electrode backplate. Step S4: Form a conductive metal layer on the surface of the patterned layered structure; Step S5: Using an etching process, multiple non-penetrating surface morphology structures are etched in the front diaphragm plate area of the movable electrode, and a gap is etched between the movable electrode and the fixed electrode, so that the side protrusion structures of the two are arranged in an alternating pattern. Step S6: After forming the movable electrode, a second sacrificial layer is formed at a preset height position of the cantilever beam of the movable electrode, and then an upper fixed electrode back plate is formed on the surface of the second sacrificial layer. Step S7: Etch the back side of the substrate to form a back cavity corresponding to the mounting areas of the movable electrode and the fixed electrode. Step S8: Remove the first sacrificial layer and the second sacrificial layer to form a first cavity and a second cavity that are interconnected.
[0011] Fifthly, a microphone device according to this embodiment includes the aforementioned MEMS transducer based on acoustic flow effect.
[0012] The beneficial effects of the embodiments of the present invention are: This MEMS transducer is designed based on the acoustic flow effect. When sound waves propagate in a medium, energy dissipation or sound field distortion can cause directional acoustic flow. When a sound wave is incident on the diaphragm plate at the front end of the movable electrode, multiple surface morphological structures (protrusions or pits) on the diaphragm plate enhance the sound field distortion, resulting in a more pronounced acoustic flow on the incident sound wave side, which drives the diaphragm plate to produce greater directional motion. Compared to traditional pressure difference-based transducers, this invention has a stronger response to sound waves, especially for low-frequency sound waves with slow phase changes, still generating considerable driving force and effectively improving low-frequency response performance.
[0013] Secondly, both the movable and fixed electrodes employ a cantilever beam structure, with one end fixed and the other free. This structure allows for a larger displacement amplitude when subjected to driving force, further improving the transducer's sensitivity. The movable electrode and the fixed electrode both feature staggered protrusions along their cantilever beam sides. This staggered arrangement increases the edge electric field line density between the two electrodes, resulting in a larger capacitance change under the same voltage, thereby enhancing the transducer's output signal strength.
[0014] Furthermore, this invention also provides a MEMS transducer with a dual-capacitor output structure. This structure has an upper fixed electrode backplate and a lower fixed electrode backplate respectively disposed on both sides of the movable electrode cantilever beam in the second direction, forming two capacitors. When the movable electrode vibrates, the values of the two capacitors change in opposite directions. Differential output can significantly improve signal strength and effectively cancel common-mode noise, further improving the signal-to-noise ratio. Simultaneously, the first cavity and the second cavity are interconnected, ensuring air pressure balance on both sides of the movable electrode and avoiding the adverse effects of air film damping on vibration. Attached Figure Description
[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.
[0016] Figure 1 This is an overall schematic diagram of the first embodiment of the MEMS transducer based on the acoustic flow effect of the present invention; Figure 2 This is a schematic diagram of the first cantilever beam and the second cantilever beam according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the structure corresponding to step S1 in the preparation method of the third embodiment of the present invention; Figure 4 This is a schematic diagram of the structure corresponding to step S2 in the preparation method of the third embodiment of the present invention; Figure 5 This is a schematic diagram of the structure corresponding to step S3 in the preparation method of the third embodiment of the present invention; Figure 6 This is a schematic diagram of the structure corresponding to step S4 in the preparation method of the third embodiment of the present invention; Figure 7 This is a schematic diagram of the structure corresponding to step S5 in the preparation method of the third embodiment of the present invention; Figure 8 This is a schematic diagram of the second embodiment of the MEMS transducer based on the acoustic flow effect of the present invention; Figure 9 This is a schematic diagram of the structure corresponding to step S1 in the preparation method of the fourth embodiment of the present invention; Figure 10 This is a schematic diagram of the structure corresponding to step S2 in the preparation method of the fourth embodiment of the present invention; Figure 11 This is a schematic diagram of the structure corresponding to step S3 in the preparation method of the fourth embodiment of the present invention; Figure 12 This is a schematic diagram of the structure corresponding to step S4 in the preparation method of the fourth embodiment of the present invention; Figure 13 This is a schematic diagram of the structure corresponding to step S5 in the preparation method of the fourth embodiment of the present invention; Figure 14 This is a schematic diagram of the structure corresponding to step S6 in the preparation method of the fourth embodiment of the present invention; Figure 15This is a schematic diagram of the structure corresponding to step S7 in the preparation method of the fourth embodiment of the present invention; Figure 16 This is a schematic diagram of the structure corresponding to step S8 in the preparation method of the fourth embodiment of the present invention; Figure 17 This is a schematic diagram of the structure corresponding to step S9 in the preparation method of the fourth embodiment of the present invention.
[0017] Icons: 1. Substrate; 2. Fixed electrode; 21. First cantilever beam; 211. First protrusion structure; 3. Movable electrode; 31. Front diaphragm plate; 32. Second cantilever beam; 33. Second protrusion structure; 4. Back cavity; 51. Insulating layer; 52. Conductive layer; 53. Surface structure; 61. Upper fixed electrode back plate; 62. Lower fixed electrode back plate; 63. First cavity; 64. Second cavity; 65. Fixed electrode cantilever beam; 71. First sacrificial layer; 72. Second sacrificial layer; 73. Metal conductive layer. Detailed Implementation
[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.
[0019] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.
[0020] It should be noted that similar labels and letters in the following figures indicate similar items. Therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures.
[0021] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," "third," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0022] Furthermore, terms such as "horizontal" and "vertical" do not imply that components must be absolutely horizontal or suspended, but rather that they can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," and does not mean that the structure must be completely horizontal, but can be slightly tilted.
[0023] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.
[0024] First Embodiment Please refer to Figure 1 and Figure 2 This embodiment provides a MEMS transducer, including a substrate 1, a fixed electrode 2, and a movable electrode 3.
[0025] The substrate 1 has a front side and a back side. The substrate 1 can be made of silicon, glass, or a silicon-glass composite material, and its thickness can be selected according to actual needs, such as 200~500μm. The substrate 1 serves as the support structure for the entire transducer, providing a mounting base for the fixed electrode 2 and the movable electrode 3.
[0026] The fixed electrode 2 is disposed on the front side of the substrate 1. The fixed electrode 2 includes a first cantilever beam 21, one end of which is fixedly connected to the front side of the substrate 1, and the other end is a free end, so that the fixed electrode 2 can generate a certain elastic deformation when subjected to external force. However, in this embodiment, the fixed electrode 2 mainly serves as a fixed reference electrode. At least one first protrusion structure 211 is provided on the side of the first cantilever beam 21. The first protrusion structure 211 can be a strip-shaped protrusion arranged at intervals along the extension direction of the cantilever beam, and its function is to form an alternating arrangement with the second protrusion structure 33 of the movable electrode 3 to enhance the edge electric field.
[0027] The movable electrode 3 is disposed on the front side of the substrate 1 and is connected to the fixed electrode 2 in a first direction (e.g., Figure 1 The movable electrodes 3 are spaced apart along the X direction shown in the diagram. The movable electrodes 3 include a front diaphragm plate 31 and a second cantilever beam 32, which are integrated together. One end of the second cantilever beam 32 is fixedly connected to the front surface of the substrate 1, and the other end is connected to the front diaphragm plate 31. The front diaphragm plate 31 is the main area of the transducer for receiving sound waves, and its surface has multiple surface structures 53 that do not penetrate its thickness. The surface structures 53 can be protrusions (such as hemispherical protrusions, columnar protrusions, or frustum-shaped protrusions) or pits (such as hemispherical pits, cylindrical pits, or frustum-shaped pits), arranged in an array to enhance the acoustic flow effect. When sound waves are incident on the front diaphragm plate 31, these microstructures distort the sound field, generating a stronger directional flow of the medium, thus producing a greater driving force on the diaphragm plate.
[0028] The second cantilever beam 32 has at least one second protrusion structure 33 on its side, and the second protrusion structure 33 is staggered with the first protrusion structure 211 in the first direction. "Staggered arrangement" means that the first protrusion structure 211 and the second protrusion structure 33 are alternately distributed in the extension direction of the cantilever beam, and do not directly contact each other, but form a comb-like interlocking structure, which significantly increases the edge electric field line density between the fixed electrode 2 and the movable electrode 3. When the movable electrode 3 vibrates, the capacitance change is greater and the output signal is stronger.
[0029] The movable electrode 3 can be positioned relative to the fixed electrode 2 along a second direction (e.g., Figure 2 The vibration occurs in the Y direction (perpendicular to the front side of substrate 1). The second direction is perpendicular to the first direction. When the movable electrode 3 vibrates, the distance between it and the fixed electrode 2 changes, causing a change in the capacitance between them. By detecting this change in capacitance, acoustic-to-electrical conversion can be achieved.
[0030] A back cavity 4 is formed on the back side of the substrate 1. The back cavity 4 can be formed by a deep silicon etching process, and its depth is 1 / 2 to 4 / 5 of the thickness of the substrate 1, for example, it can be etched to a remaining thickness of 50~200μm. The projection area of the back cavity 4 on the front side of the substrate 1 covers the mounting area of the movable electrode 3 and the fixed electrode 2, thereby providing space for the vibration of the movable electrode 3, reducing air damping, and improving vibration sensitivity.
[0031] In this embodiment, the MEMS transducer operates based on the acoustic flow effect. When sound waves are incident from one side of the front diaphragm plate 31, the surface structure 53 of the diaphragm plate distorts the sound field, generating a directional acoustic flow along the diaphragm plate surface. The acoustic flow pushes the front diaphragm plate 31, causing it to drive the second cantilever beam 32 to bend and vibrate in a second direction (perpendicular to the front side of the substrate 1). Since the second cantilever beam 32 has a second protrusion structure 33 on its side and the first cantilever beam 21 of the fixed electrode 2 has a first protrusion structure 211 on its side, the two are arranged alternately. When the second cantilever beam 32 vibrates, the edge electric field between it and the first cantilever beam 21 changes drastically, resulting in a significant change in the capacitance value between the movable electrode 3 and the fixed electrode 2. By detecting this capacitance change, the sound signal can be detected. Compared with traditional transducers based on pressure difference, this embodiment can still generate sufficient driving force for low-frequency sound waves, effectively improving low-frequency response performance.
[0032] In a preferred embodiment, both the movable electrode 3 and the fixed electrode 2 are multilayer composite layered structures. Specifically, each composite layered structure is formed by alternating stacks of insulating layer 51 and conductive layer 52. The insulating layer 51 can be made of one or more combinations of silicon, silicon oxide, silicon nitride, and polymer; the conductive layer 52 can be made of one or more combinations of silicon, doped silicon, polycrystalline silicon, amorphous silicon, aluminum, copper, gold, and tungsten. The multilayer composite structure can be designed with different numbers of layers and material combinations according to actual needs to optimize the mechanical and electrical properties of the electrodes. For example, the conductive layer 52 is used to form capacitor plates, and the insulating layer 51 is used to ensure electrical isolation between the electrodes while providing mechanical support.
[0033] In this embodiment, the multilayered composite structure enables the movable electrode 3 and the fixed electrode 2 to possess both good electrical conductivity and suitable mechanical stiffness. By adjusting the thickness and material of each layer, the elastic coefficient of the cantilever beam can be precisely controlled, allowing it to generate an appropriate vibration amplitude under acoustic flow drive while ensuring sufficient structural strength. The alternating stacking of the insulating layer 51 and the conductive layer 52 can also reduce stress concentration and improve the reliability of the device.
[0034] In a preferred embodiment, the surface structure 53 can be a raised structure or a recessed structure, arranged in an array. The raised structure can be one of a hemispherical raised structure, a columnar raised structure, or a frustum-shaped raised structure; the recessed structure can be one of a hemispherical recessed structure, a cylindrical recessed structure, or a frustum-shaped recessed structure. The first raised structure 211 and the second raised structure 33 are both strip-shaped raised structures, which are arranged at equal or unequal intervals along the extension direction of the cantilever beam, and the distance between adjacent strip-shaped raised structures can be 5~20μm.
[0035] In this embodiment, the array arrangement and diverse shape design of the surface structures 53 can be optimized according to the actual application scenario. For example, for sound waves in a specific frequency range, a specific shape and arrangement density of the surface structures 53 can be selected to enhance the acoustic flow effect. The staggered arrangement of the strip protrusions can be optimized according to the size and vibration characteristics of the cantilever beam to obtain the maximum capacitance change. Equal spacing is beneficial for process implementation and electric field uniformity, while unequal spacing can be optimized for specific vibration modes.
[0036] In a preferred embodiment, the back cavity 4 is a groove structure formed by deep silicon etching process. The depth of the back cavity 4 is 1 / 2 to 4 / 5 of the thickness of the substrate 1. After etching, the remaining thickness between the front surface of the substrate 1 and the bottom surface of the back cavity 4 is 50~200μm.
[0037] In this embodiment, the depth of the back cavity 4 is selected based on the following considerations: if the depth is too shallow, the vibration space for the movable electrode 3 is insufficient, making it prone to contact with the substrate 1; if the depth is too deep, it will weaken the mechanical strength of the substrate 1 and increase the processing difficulty. A remaining thickness of 50~200μm can ensure sufficient support strength for the substrate 1 while providing sufficient vibration space for the movable electrode 3. Deep silicon etching processes (such as the Bosch process) can form vertical sidewalls with high aspect ratios, which is beneficial for precisely controlling the size and shape of the back cavity 4.
[0038] Second Embodiment Please refer to Figure 8 This embodiment provides a MEMS transducer, which includes a substrate 1, a movable electrode 3, an upper fixed electrode backplate 61, and a lower fixed electrode backplate 62. The substrate 1 has a front side and a back side. The material and structure of the substrate 1 are similar to those of the first embodiment, and will not be described again here.
[0039] A movable electrode 3 is disposed on the front side of the substrate 1, including a front diaphragm plate 31 and a cantilever beam, with the front diaphragm plate 31 and the cantilever beam connected as a single unit. One end of the cantilever beam is fixedly connected to the front side of the substrate 1. The surface of the front diaphragm plate 31 is provided with a plurality of surface structures 53 that do not penetrate its thickness. The surface structures 53 serve the same function as in the first embodiment, for enhancing the acoustic flow effect.
[0040] The upper fixed electrode back plate 61 is disposed on one side (i.e., the upper side) of the cantilever beam of the movable electrode 3 in the second direction (the direction perpendicular to the front side of the substrate 1) and is fixedly connected to the substrate 1. The lower fixed electrode back plate 62 is disposed on the other side (i.e., the lower side) of the cantilever beam of the movable electrode 3 in the second direction and is fixedly connected to the substrate 1. Both the upper fixed electrode back plate 61 and the lower fixed electrode back plate 62 are multi-layered composite layered structures, which are formed by alternating stacking of insulating layer 51 and conductive layer 52.
[0041] A first cavity 63 is formed between the movable electrode 3 and the upper fixed electrode back plate 61, and a second cavity 64 is formed between the movable electrode 3 and the lower fixed electrode back plate 62. The first cavity 63 and the second cavity 64 are interconnected through a connecting channel. The height of the first cavity 63 can be 1~5μm, the height of the second cavity 64 can be 1~5μm, and the width of the connecting channel can be 10~50μm, and the width of the connecting channel is smaller than the width of the cantilever beam of the movable electrode 3.
[0042] The movable electrode 3 can vibrate in the second direction to simultaneously change the first capacitance value between the movable electrode 3 and the upper fixed electrode back plate 61, and the second capacitance value between the movable electrode 3 and the lower fixed electrode back plate 62.
[0043] A back cavity 4 is provided on the back side of the substrate 1, and the projection area of the back cavity 4 on the front side of the substrate 1 covers the mounting area of the movable electrode 3.
[0044] In this embodiment, the MEMS transducer operates as follows: When sound waves are incident on the front diaphragm plate 31, the surface structure 53 enhances the acoustic flow effect, driving the front diaphragm plate 31 to cause the cantilever beam to vibrate along the second direction. During cantilever beam vibration, the distance between it and the upper fixed electrode back plate 61 and the distance between it and the lower fixed electrode back plate 62 change in opposite directions: when the cantilever beam vibrates upwards, the first cavity 63 decreases and the second cavity 64 increases, thus increasing the first capacitance value and decreasing the second capacitance value; when the cantilever beam vibrates downwards, the first capacitance value decreases and the second capacitance value increases. By detecting the changes in these two capacitance values differentially, a signal strength twice that of a single-capacitor structure can be obtained, while simultaneously canceling common-mode noise and significantly improving the signal-to-noise ratio. Furthermore, the first cavity 63 and the second cavity 64 are interconnected through a connecting channel, ensuring air pressure balance on both sides of the cantilever beam, avoiding the obstruction of vibration by air film damping, and thus improving high-frequency response performance.
[0045] In a preferred embodiment, the MEMS transducer further includes a fixed electrode cantilever beam 65. The fixed electrode cantilever beam 65 is disposed on the side of the cantilever beam of the movable electrode 3 in a first direction (i.e., the horizontal side) and is fixedly connected to the front surface of the substrate 1. The side of the fixed electrode cantilever beam 65 has at least one third protrusion structure, and the side of the cantilever beam of the movable electrode 3 has at least one fourth protrusion structure. The third and fourth protrusion structures are staggered in the first direction. This structure is similar to the side protrusion structures of the fixed electrode 2 and the movable electrode 3 in the first embodiment, which can further enhance the capacitance change and improve the output signal.
[0046] In this embodiment, the fixed electrode cantilever beam 65 enables the MEMS transducer to simultaneously possess a vertical dual-capacitor structure and a horizontal edge capacitor structure. When the movable electrode 3 vibrates, not only do the two capacitors in the vertical direction change in opposite directions, but the capacitance between the horizontal electrode and the fixed electrode cantilever beam 65 also changes. Through the combined detection of multiple capacitors, signal strength and sensitivity can be further improved. This composite structure is particularly suitable for applications requiring high sensitivity.
[0047] In a preferred embodiment, both the upper fixed electrode back plate 61 and the lower fixed electrode back plate 62 are multi-layered composite structures, formed by alternating stacks of insulating layer 51 and conductive layer 52. The first cavity 63 and the second cavity 64 are interconnected by a connecting channel, the width of which is smaller than the width of the cantilever beam of the movable electrode 3.
[0048] In this embodiment, the multi-layered composite structure provides the fixed electrode 2 backplate with good conductivity and mechanical stability. The cavity height (1~5μm) is chosen to ensure both sufficient vibration space and a sufficiently large capacitance. The width of the connecting channel is smaller than the width of the cantilever beam, which ensures air pressure balance on both sides of the cantilever beam without affecting its structural strength.
[0049] Third Embodiment Please refer to Figures 3 to 7 This embodiment provides a method for fabricating a MEMS transducer, used to fabricate the MEMS transducer described in the first embodiment. The method includes the following steps: Step S1: Provide substrate 1. The substrate 1 can be made of silicon, glass, or a silicon-glass composite material, with a thickness of 200~500μm. As the substrate for subsequent processes, the surface of substrate 1 needs to be cleaned and pretreated to ensure good adhesion.
[0050] Step S2: A first insulating layer 51, a conductive layer 52, and a second insulating layer 51 are sequentially deposited on the front side of substrate 1. The first insulating layer 51, conductive layer 52, and second insulating layer 51 are then patterned to form the basic outline of the movable electrode 3 and the fixed electrode 2. The deposition process can be chemical vapor deposition (CVD) or physical vapor deposition (PVD). The insulating layer 51 can be made of one or more combinations of silicon oxide, silicon nitride, and polyimide, with a thickness of 0.5~2μm. The conductive layer 52 can be made of one of polycrystalline silicon, doped silicon, aluminum, and copper, with a thickness of 0.3~1.5μm. The patterning process uses photolithography, defining the planar shape of the electrodes using a photomask, including the outline of the cantilever beam and the position of the side protrusions.
[0051] Step S3: Form a conductive metal layer 73 on the surface of the patterned layered structure. Specifically, a metal material can be sputtered using magnetron sputtering. The metal material can be one or more combinations of titanium, chromium, tungsten, aluminum, gold, copper, and platinum, with a thickness of 0.1~0.5μm. Then, a photolithography process is used to pattern the metal material to form the conductive metal layer 73. The conductive metal layer 73 can reduce the contact resistance of the electrodes and improve conductivity.
[0052] Step S4: Using an etching process, multiple non-penetrating surface structures 53 are etched in the front diaphragm plate 31 region of the movable electrode 3, and a gap is etched between the movable electrode 3 and the fixed electrode 2, so that the side protrusions of the two are arranged in an alternating pattern. The etching depth of the surface structures 53 is 1 / 3 to 2 / 3 of the overall thickness of the front diaphragm plate 31 to ensure structural strength while obtaining sufficient acoustic flow enhancement effect. The width of the gap can be 5~20μm. The etching process can use dry etching (such as reactive ion etching, RIE) to achieve high precision and high aspect ratio.
[0053] Step S5: Etch the back side of substrate 1 to form a back cavity 4 corresponding to the mounting areas of movable electrode 3 and fixed electrode 2. Specifically, a deep silicon etching process (such as the Bosch process) can be used, with an etching depth of 1 / 2 to 4 / 5 of the thickness of substrate 1, for example, etching to a remaining thickness of 50~200μm. The deep silicon etching process can form vertical sidewalls and precisely control the size of the back cavity 4.
[0054] The above steps complete the fabrication of the MEMS transducer described in the first embodiment.
[0055] Fourth embodiment refer to Figures 9 to 17 This embodiment also provides a method for fabricating a MEMS transducer, used to fabricate the MEMS transducer described in the second embodiment. Based on steps S1 to S5 above, this method further includes the following additional steps: Step S2a: Following step S2, a lower fixed electrode backplate 62 is formed at a predetermined position on the front side of the substrate 1, and a first sacrificial layer 71 is formed on the surface of the lower fixed electrode backplate 62. The formation process of the lower fixed electrode backplate 62 can be similar to the electrode formation process in step S2, employing a multilayer composite layered structure. The material of the first sacrificial layer 71 can be polyimide or photoresist, with a thickness of 1~5μm, used for the subsequent formation of the second cavity 64.
[0056] Step S4a: After step S4, a second sacrificial layer 72 is formed at a predetermined height position of the cantilever beam of the movable electrode 3, and then an upper fixed electrode backplate 61 is formed on the surface of the second sacrificial layer 72. The material of the second sacrificial layer 72 can also be polyimide or photoresist, with a thickness of 1~5μm, for subsequent formation of the first cavity 63. The formation process of the upper fixed electrode backplate 61 is similar to that of the lower fixed electrode backplate 62.
[0057] Step S5a: After step S5, the first sacrificial layer 71 and the second sacrificial layer 72 are removed using a wet etching or dry etching process to form a first cavity 63 and a second cavity 64 that are interconnected. Then, the device is subjected to surface passivation treatment to protect the device from environmental corrosion.
[0058] The above steps complete the fabrication of the MEMS transducer described in the second embodiment.
[0059] Fifth Embodiment This embodiment also provides a microphone device, including the MEMS transducer in the first or second embodiment. The transducer is designed based on the acoustic flow effect. Compared with traditional transducers based on pressure difference, the present invention has a stronger response to sound waves, especially for low-frequency sound waves with slow phase changes, and can still generate considerable driving force, effectively improving low-frequency response performance.
[0060] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A MEMS transducer based on the acoustic flow effect, characterized in that, include: A substrate having a front side and a back side; A fixed electrode is disposed on the front side of the substrate. The fixed electrode includes a first cantilever beam, one end of which is fixedly connected to the substrate and the other end is a free end. A first protrusion structure is provided on the side of the first cantilever beam. A movable electrode is disposed on the front side of the substrate and spaced apart from the fixed electrode in a first direction. The movable electrode includes a front diaphragm plate and a second cantilever beam integrally connected. One end of the second cantilever beam is fixedly connected to the substrate. The surface of the front diaphragm plate is provided with a plurality of surface structures that do not penetrate its thickness. The side of the second cantilever beam is provided with a second protrusion structure. The second protrusion structure and the first protrusion structure are arranged alternately in the first direction. The movable electrode is capable of vibrating relative to the fixed electrode in a second direction to change the capacitance value between the movable electrode and the fixed electrode. A back cavity is formed on the back side of the substrate, and the projection area of the back cavity on the front side of the substrate covers the mounting areas of the movable electrode and the fixed electrode.
2. The MEMS transducer based on acoustic flow effect according to claim 1, characterized in that, Both the movable electrode and the fixed electrode are multi-layered composite layered structures, which are formed by alternating stacking of insulating and conductive layers.
3. The MEMS transducer based on acoustic flow effect according to claim 2, characterized in that, The surface structure is a raised structure or a recessed structure, and the surface structure is arranged in an array; the first raised structure and the second raised structure are both strip-shaped raised structures, and the strip-shaped raised structures are arranged along the extension direction of the cantilever beam.
4. The MEMS transducer based on acoustic flow effect according to claim 2, characterized in that, The back cavity is a groove structure formed by deep silicon etching process, and the depth of the back cavity is 1 / 2 to 4 / 5 of the thickness of the substrate.
5. A MEMS transducer based on the acoustic flow effect, characterized in that, include: A substrate having a front side and a back side; A movable electrode is disposed on the front side of the substrate and includes an integrally connected front diaphragm plate and a cantilever beam. One end of the cantilever beam is fixedly connected to the front side of the substrate. The surface of the front diaphragm plate is provided with multiple surface structures that do not penetrate its thickness. An upper fixed electrode back plate is provided, which is disposed on one side of the cantilever beam of the movable electrode and is fixedly connected to the substrate. A lower fixed electrode back plate is provided, which is disposed on the other side of the cantilever beam of the movable electrode and is fixedly connected to the substrate. A first cavity is formed between the movable electrode and the upper fixed electrode back plate, and a second cavity is formed between the movable electrode and the lower fixed electrode back plate. The first cavity and the second cavity are interconnected. The movable electrode can vibrate in the second direction to simultaneously change the first capacitance value between the movable electrode and the upper fixed electrode back plate, and the second capacitance value between the movable electrode and the lower fixed electrode back plate. A back cavity is formed on the back side of the substrate, and the projection area of the back cavity on the front side of the substrate covers the mounting area of the movable electrode.
6. The MEMS transducer based on the acoustic flow effect according to claim 5, characterized in that, Both the upper fixed electrode backplate and the lower fixed electrode backplate are multi-layered composite layered structures, which are formed by alternating stacking of insulating and conductive layers; the first cavity and the second cavity are interconnected through a connecting channel, the width of which is smaller than the width of the cantilever beam of the movable electrode.
7. A fabrication method, applied to the MEMS transducer based on the acoustic flow effect as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step S1: Provide a substrate; Step S2: Sequentially deposit a first insulating layer, a conductive layer, and a second insulating layer on the front side of the substrate, and perform patterning processing on the first insulating layer, the conductive layer, and the second insulating layer to form the basic outline of the movable electrode and the fixed electrode. Step S3: Form a conductive metal layer on the surface of the patterned layered structure; Step S4: Using an etching process, multiple non-penetrating surface structures are etched in the diaphragm plate area at the front end of the movable electrode, and a gap is etched between the movable electrode and the fixed electrode, so that the side protrusion structures of the two are arranged in an alternating pattern. Step S5: Etch the back side of the substrate to form a back cavity corresponding to the mounting areas of the movable electrode and the fixed electrode.
8. The preparation method according to claim 7, characterized in that, In step S2, the deposition process is chemical vapor deposition or physical vapor deposition; in step S3, the process for forming the metal conductive layer is sputtering; in step S4, the depth of etching the surface structure is 1 / 3 to 2 / 3 of the overall thickness of the front-end diaphragm plate. In step S5, the depth of the back cavity is 1 / 2 to 4 / 5 of the thickness of the substrate.
9. A fabrication method, applied to the MEMS transducer as described in any one of claims 5 to 6, characterized in that, include: Step S1: Provide a substrate; Step S2: Sequentially deposit a first insulating layer, a conductive layer, and a second insulating layer on the front side of the substrate, and perform patterning processing on the first insulating layer, the conductive layer, and the second insulating layer to form the basic outline of the movable electrode and the fixed electrode. Step S3: A lower fixed electrode backplate is formed at a predetermined position on the front side of the substrate, and a first sacrificial layer is formed on the surface of the lower fixed electrode backplate. Step S4: Form a conductive metal layer on the surface of the patterned layered structure; Step S5: Using an etching process, multiple non-penetrating surface morphology structures are etched in the front diaphragm plate area of the movable electrode, and a gap is etched between the movable electrode and the fixed electrode, so that the side protrusion structures of the two are arranged in an alternating pattern. Step S6: After forming the movable electrode, a second sacrificial layer is formed at a preset height position of the cantilever beam of the movable electrode, and then an upper fixed electrode back plate is formed on the surface of the second sacrificial layer. Step S7: Etch the back side of the substrate to form a back cavity corresponding to the mounting areas of the movable electrode and the fixed electrode. Step S8: Remove the first sacrificial layer and the second sacrificial layer to form a first cavity and a second cavity that are interconnected.
10. A microphone device, characterized in that, Includes MEMS transducers based on acoustic flow effect as described in any one of claims 1 to 4 or 5 to 6.