Piezoelectric MEMS microphone and preparation method thereof

Abstract

The invention provides a piezoelectric MEMS microphone and a preparation method thereof. The piezoelectric MEMS microphone comprises a substrate, a vibrating diaphragm, n cantilever beams and n first piezoelectric units. Wherein the substrate is provided with a cavity penetrating through the thickness direction, and the cavity is in a regular n prism shape; the vibrating diaphragm is a regular n-polygon, and the vibrating diaphragm and the substrate are coaxially arranged and are located on one side of the cavity; the n cantilever beams are distributed in a radiation array mode, one end of each cantilever beam is connected to the corresponding vertex position of the vibrating diaphragm, and the other end of each cantilever beam is connected to the middle position of the corresponding side line of the opening end of the cavity. And the n first piezoelectric units are respectively and correspondingly fixed on the n cantilever beams, and n is greater than or equal to 6. And when the sound pressure drives the vibrating diaphragm to generate vibration displacement along the thickness direction of the substrate to drive the cantilever beam to generate strain, the first piezoelectric unit positioned on the cantilever beam generates an electric signal through a piezoelectric effect. That is, the vibrating diaphragm enables each first piezoelectric unit located on the cantilever beam to generate a piezoelectric signal, thereby remarkably improving the sensitivity, frequency response and other performances of the microphone.

Description

Technical Field

[0001] This invention relates to the field of acoustic sensor technology, specifically providing a piezoelectric MEMS microphone and its fabrication method. Background Technology

[0002] MEMS microphones, due to their small size, low power consumption, and mass production capabilities, have gradually replaced traditional electret microphones (ECMs) and are widely used in voice interaction, environmental monitoring, and other fields. Currently, mainstream MEMS microphones are mainly divided into two categories: condenser and piezoelectric. Condenser MEMS microphones, based on the principle of variable capacitance, require an external bias voltage and have high sensitivity, but are susceptible to electromagnetic interference (EMI), and their signal conditioning circuitry is complex. Piezoelectric MEMS microphones utilize the positive piezoelectric effect of piezoelectric materials, requiring no bias voltage and exhibiting strong anti-interference capabilities. However, traditional designs are limited by the diaphragm structure, resulting in insufficient sensitivity or nonlinear frequency response.

[0003] As the core transducer structure, the shape of the diaphragm directly affects the microphone's sensitivity, frequency response, and reliability. In existing technologies, diaphragms primarily employ circular or square designs: circular diaphragms offer the best symmetry and uniform stress distribution, but are prone to resonance peaks in the high-frequency range, and the edge-fixing process is more challenging (requiring precise control of etching roundness). Square diaphragms offer good compatibility with CMOS processes, but significant stress concentration at the corners can lead to fatigue fracture with long-term use, and they also exhibit complex asymmetric vibration modes. Summary of the Invention

[0004] The purpose of this invention is to solve the problem of poor performance of existing MEMS microphones due to limitations in diaphragm structure, such as poor sensitivity or frequency response.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] This invention provides a piezoelectric MEMS microphone, comprising: a substrate having a cavity extending through its thickness direction, the cavity being a regular n-prism; a diaphragm being a regular n-sided polygon, the diaphragm being coaxially disposed with the substrate and located on one side of the cavity; n cantilever beams arranged in a radial array, one end of each cantilever beam being connected to a corresponding vertex position of the diaphragm, and the other end of each cantilever beam being connected to the middle position of a corresponding edge of the cavity opening; and n first piezoelectric units, each corresponding to and fixed on one of the n cantilever beams; wherein n is an even number not less than 6, when sound pressure drives the diaphragm to vibrate and displace along the thickness direction of the substrate, causing strain in the cantilever beams, the first piezoelectric units located on the cantilever beams generate electrical signals through the piezoelectric effect.

[0007] Preferably, the diaphragm is integrally formed with the cantilever beam.

[0008] Preferably, both the diaphragm and the cantilever beam are located at the open end of the cavity, and the first piezoelectric unit is disposed away from the cavity.

[0009] Preferably, the device further includes a second piezoelectric unit disposed on the diaphragm, the second piezoelectric unit being coaxially disposed with the diaphragm, and the second piezoelectric unit and the first piezoelectric stack structure being located on the same side of the diaphragm.

[0010] Preferably, the second piezoelectric unit is a regular n-sided polygon similar in shape to the diaphragm, the second piezoelectric unit is located in the central region of the diaphragm, and the radial dimension of the second piezoelectric unit is smaller than the radial dimension of the diaphragm.

[0011] Preferably, the radial dimension of the second piezoelectric unit is 1 / 5 to 2 / 5 of the radial dimension of the diaphragm.

[0012] Preferably, the second piezoelectric unit is an annular frame with a regular n-sided shape, and the annular frame is located in the edge region of the diaphragm.

[0013] Preferably, along the radial direction of the diaphragm, the width of the annular frame is 1 / 10 to 1 / 5 of the radial dimension of the diaphragm, and the annular frame is located at the edge of the diaphragm and recessed inward by 1 / 10 to 1 / 5 of the radial dimension of the diaphragm.

[0014] Preferably, the length direction of the first piezoelectric unit is consistent with the radiation direction of the cantilever beam. The first piezoelectric unit includes a first piezoelectric thin film layer and a first electrode layer and a second electrode layer located on both sides of the first piezoelectric thin film layer. The second electrode layer is fixed at the middle position in the width direction of the cantilever beam. The width of the first piezoelectric thin film layer is the same as the width of the second electrode layer. The width of the first electrode layer is 70% ± 5% of the width of the second electrode layer.

[0015] Preferably, n first electrode layers are connected in parallel to output electrical signals, and n second electrode layers are integrally formed and connected in parallel to output electrical signals.

[0016] Preferably, when n is an even number, the two first piezoelectric units that are symmetrically positioned in the radial direction of the radiation array are divided into n / 2 differential pairs. Each differential pair is isolated from each other, and the electrical signals collected by each differential pair are differentially amplified.

[0017] Preferably, the material of the first piezoelectric thin film layer includes any one of aluminum nitride, zinc oxide, and lead zirconate titanate; and / or the materials of the first electrode layer and the second electrode layer both include any one of molybdenum, gold, aluminum, and chromium.

[0018] Preferably, the diaphragm material comprises silicon nitride or silicon oxide; and / or the cantilever beam material comprises silicon nitride or silicon oxide; and / or the substrate material comprises silicon oxide or single-crystal silicon.

[0019] Based on the same inventive concept, the present invention also provides a method for fabricating the piezoelectric MEMS microphone, characterized in that it includes:

[0020] S1. A thin film layer is deposited on a substrate using plasma-enhanced chemical vapor deposition (PECVD) and a regular n-sided diaphragm and n radially distributed cantilever beams are designed.

[0021] S2. Using selective deposition or patterning processes, n corresponding first piezoelectric units are deposited in the planned n cantilever beam regions respectively;

[0022] S3. Use photolithography and metal deposition processes to etch the leads and pads that are electrically connected to the first piezoelectric unit;

[0023] S4. Using photolithography and deep reactive ion technology, a cavity of a regular n-prism is etched on the back side of the substrate, which is coaxially arranged with the diaphragm and the cantilever beams. The diaphragm and n cantilever beams are then released to obtain a piezoelectric MEMS microphone.

[0024] Based on the same inventive concept, the present invention also provides an electronic device, including the aforementioned piezoelectric MEMS microphone.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention provides a piezoelectric MEMS microphone, comprising a substrate, a diaphragm, n cantilever beams, and n first piezoelectric units. The substrate has a cavity extending through its thickness, and the cavity is a regular n-prism. The diaphragm is a regular n-sided polygon, coaxially positioned with the substrate and located on one side of the cavity. The n cantilever beams are arranged in a radial array, with one end of each cantilever beam connected to the vertex of the diaphragm and the other end connected to the middle of the opening edge of the cavity. The n first piezoelectric units are respectively attached to and fixed on the n cantilever beams. n is an even number not less than 6. When sound pressure drives the diaphragm to vibrate and displace along the thickness direction of the substrate, causing strain in the cantilever beams, the first piezoelectric units on the cantilever beams generate electrical signals through the piezoelectric effect. This configuration, combining a polygonal diaphragm with a radial cantilever beam, optimizes the vibration modes and amplifies the mechanical strain of the cantilever beam lever. The diaphragm ensures that each of the first piezoelectric units on the cantilever beam generates a piezoelectric signal, enhancing the piezoelectric conversion efficiency of the first piezoelectric unit and significantly improving the microphone's performance in terms of sensitivity, frequency response, and signal-to-noise ratio. Furthermore, the diaphragm's symmetrical polygonal design ensures uniform stress distribution, facilitating fabrication and integration. Attached Figure Description

[0027] Figure 1 This is a three-dimensional structural schematic diagram of Embodiment 1 of the piezoelectric MEMS microphone of the present invention;

[0028] Figure 2 This is a top view of Embodiment 1 of the piezoelectric MEMS microphone of the present invention;

[0029] Figure 3 for Figure 2 Schematic diagram of the structure in the AA section;

[0030] Figure 4 This is a three-dimensional structural schematic diagram of Embodiment 2 of the piezoelectric MEMS microphone of the present invention;

[0031] Figure 5 This is a top view of Embodiment 2 of the piezoelectric MEMS microphone of the present invention;

[0032] Figure 6 for Figure 5 Schematic diagram of the structure in the AA section;

[0033] Figure 7 This is a top view of embodiment 3 of the piezoelectric MEMS microphone of the present invention;

[0034] Figure 8 This is a schematic diagram of the first electrode connection circuit for Embodiment 2 of the piezoelectric MEMS microphone.

[0035] Reference numerals: 1-Substrate; 10-Cavity; 2-Diaphragm; 3-Cantilever Beam; 4-First Piezoelectric Unit; 41-First Piezoelectric Thin Film Layer; 42-First Electrode Layer; 43-Second Electrode Layer; 5-Second Piezoelectric Unit; 51-Second Piezoelectric Thin Film Layer; 52-Third Electrode Layer; 53-Fourth Electrode Layer; 6-Annular Frame; 71-First Pad; 72-Second Pad; 81-Third Pad; 82-Fourth Pad. Detailed Implementation

[0036] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are merely illustrative of the technical principles of the invention and are not intended to limit the scope of protection of the invention. Those skilled in the art can make adjustments as needed to adapt to specific applications.

[0037] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" 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.

[0038] It should be noted that in the description of this invention, terms such as "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," indicating directional or positional relationships, are based on the directional or positional relationships shown in the accompanying drawings. These are merely for ease of description and do not indicate or imply that the device or element must have a specific orientation, or be constructed and operated in a specific orientation; therefore, they should not be construed as limitations on this invention. Furthermore, the terms "first," "second," "third," and "fourth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0039] like Figure 1 As shown, this invention provides a piezoelectric MEMS microphone, including a substrate 1, a diaphragm 2, n cantilever beams 3, and n first piezoelectric units 4. The substrate 1 has a cavity 10 extending through its thickness direction, and the cavity 10 is a regular n-prism. The diaphragm 2 is a regular n-sided polygon, coaxially arranged with the substrate 1 and located on one side of the cavity 10. The n cantilever beams 3 are arranged in a radial array, with one end of each cantilever beam 3 connected to the corresponding vertex position of the diaphragm 2, and the other end of each cantilever beam 3 connected to the middle position of the corresponding edge of the opening end of the cavity 10. The n first piezoelectric units 4 are respectively corresponding to and fixed on the n cantilever beams 3. n is an even number not less than 6. When the sound pressure drives the diaphragm 2 to vibrate and displace along the thickness direction of the substrate 1, causing strain in the cantilever beams 3, the first piezoelectric units 4 located on the cantilever beams 3 generate electrical signals through the piezoelectric effect.

[0040] With this configuration, the diaphragm 2 at the center of the microphone deforms in tandem with multiple cantilever beams 3, significantly increasing the microphone's sound pressure dynamic range. At low sound pressure levels, the diaphragm 2, with its low stiffness, dominates the vibration response, ensuring high sensitivity to weak sound waves. As the sound pressure increases, the cantilever beams 3, through their unique strain amplification and nonlinear stiffness effect, effectively suppress excessive displacement of the diaphragm 2, preventing signal saturation distortion. This adaptive working mechanism allows the microphone to accurately capture weak sounds while also withstanding high sound pressure inputs, greatly improving the sound pressure dynamic range compared to traditional designs and significantly enhancing the microphone's performance in terms of sensitivity, frequency response, and signal-to-noise ratio.

[0041] The diaphragm 2 of the piezoelectric MEMS microphone of the present invention can be hexagonal, octagonal, dodecagonal, or even an even number of other polygons.

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the following description, taking an n value of 8 as an example, in conjunction with specific embodiments and with reference to the accompanying drawings, provides a detailed explanation of this invention.

[0043] Example 1

[0044] like Figures 1 to 3 As shown, the piezoelectric MEMS microphone provided in this embodiment of the invention includes a substrate 1, a diaphragm 2, eight cantilever beams 3, and eight first piezoelectric units 4. The substrate 1 has a cavity 10 extending through its thickness direction, and the cavity 10 is a regular octagonal prism. The diaphragm 2 is a regular octagon, coaxially arranged with the substrate 1 and located on the upper side of the cavity 10. The eight cantilever beams 3 are arranged in a radial array, with one end of each cantilever beam 3 connected to the corresponding vertex position of the diaphragm 2, and the other end of each cantilever beam 3 connected to the middle position of the corresponding edge of the opening end of the cavity 10. The eight first piezoelectric units 4 are respectively corresponding to and fixed on the eight cantilever beams 3.

[0045] When the sound pressure drives the diaphragm 2 to vibrate and displace along the thickness direction of the substrate 1, causing the eight cantilever beams 3 to simultaneously generate strain, all the first piezoelectric units 4 will generate electrical signals, significantly improving the microphone's sensitivity and frequency response performance.

[0046] That is, the octagonal diaphragm 2 and the eight cantilever beams 3 work together. When sound waves act on the diaphragm 2, the octagonal diaphragm 2 undergoes symmetrical bending vibration under the driving force of the sound pressure difference. At the same time, the eight radially arranged cantilever beams 3 vibrate with the diaphragm 2, generating a lever amplification effect, which significantly enhances the local strain of the cantilever beams 3. In the piezoelectric conversion stage, the first piezoelectric unit 4 located on the cantilever beam 3 efficiently converts the mechanical strain of the cantilever beam 3 into electric charge. All the first piezoelectric units 4 together output an electrical signal corresponding to the sound pressure, realizing the high-sensitivity and wide-band loudness sound-to-electric conversion of the microphone.

[0047] The radial dimension of the diaphragm 2 is 70%-85% of the radial dimension of the cavity 10 to ensure the effective vibration of the diaphragm 2.

[0048] like Figure 2As shown, the first piezoelectric unit 4 of this embodiment is generally rectangular in shape, and the length direction of the first piezoelectric unit 4 is consistent with the radiation direction of the cantilever beam 3. In the thickness direction, the first piezoelectric unit 4 includes a first piezoelectric thin film layer 41 and a first electrode layer 42 and a second electrode layer 43 located on both sides of the first piezoelectric thin film layer 41. The second electrode layer 43 is fixed at the middle position in the width direction of the cantilever beam 3. The width of the first piezoelectric thin film layer 41 is the same as the width of the second electrode layer 43, and the width of the first electrode layer 42 is 70% ± 5% of the width of the second electrode layer 43.

[0049] The length of the second electrode layer 43 is greater than the length of the first piezoelectric thin film layer 41 so that the second electrode layer 43 can be connected to the external circuit lead.

[0050] That is, the length and width of the first piezoelectric unit 4 are consistent with the length and width of the cantilever beam 3 in the plane, and the width of the first electrode layer 42 is 70% ± 5% of the width of the second electrode layer 43. With this arrangement, under the premise that the micro-strain of the first piezoelectric unit 4 and the cantilever beam 3 are consistent, the edge region of the first piezoelectric thin film layer 41 can maintain free deformation, improve the charge collection efficiency under unit strain, and avoid the first piezoelectric thin film layer 41 being completely covered by the first electrode layer 42, which would lead to strain constraint and affect the amount of charge generated.

[0051] The diaphragm 2 material in this embodiment of the invention includes silicon nitride or silicon oxide, the cantilever beam 3 material includes silicon nitride or silicon oxide, and the substrate 1 material includes silicon oxide or single crystal silicon.

[0052] The material of the first piezoelectric thin film layer 41 in this embodiment of the invention includes any one of aluminum nitride, zinc oxide, and lead zirconate titanate; and the material of the first electrode layer 42 includes any one of molybdenum, gold, aluminum, and chromium, and the material of the second electrode layer 43 includes any one of molybdenum, gold, aluminum, and chromium.

[0053] The embodiments of the present invention also include a first pad 71 and a second pad 72, each first electrode layer 42 being electrically connected to the first pad 71, and each second electrode layer 43 being electrically connected to the second pad 72.

[0054] That is, such as Figure 8 As shown, all the first electrode layers 42 of the eight first piezoelectric units 4 are connected in parallel to the first pad 71, and all the second electrode layers 43 are connected in parallel to the second pad 72. This parallel connection increases the total capacitance of the first piezoelectric units 4, reduces the output impedance, facilitates matching with subsequent amplifiers, reduces signal transmission loss, and effectively ensures the microphone's sensitivity to sound pressure level acquisition. The first pad 71 and the second pad 72 facilitate the synchronous acquisition of piezoelectric signals generated by all the first piezoelectric units 4, making it convenient to connect to external circuits.

[0055] like Figure 3As shown, in this embodiment of the invention, the diaphragm 2 and the cantilever beam 3 are integrally formed, and all the second electrode layers 43 are integrally formed, that is, the electrode layers are directly deposited radially outward in all regions of the cantilever beam 3 to form an integral structure, thus forming all the second electrode layers 43 in parallel. This configuration simplifies the microphone manufacturing process, reduces manufacturing costs, and improves production efficiency.

[0056] like Figure 3 As shown, in this embodiment of the invention, the diaphragm 2 and the cantilever beam 3 are both located at the open end of the cavity 10, and the first piezoelectric unit 4 is disposed away from the cavity 10. Specifically, the diaphragm 2 and the cantilever beam 3 are arranged parallel to the open end face of the cavity 10, and the first piezoelectric unit 4 is located on the outside of the cavity 10. This arrangement facilitates the layout design of the first piezoelectric unit 4 and its external connections.

[0057] Example 2

[0058] Based on Example 1, such as Figures 4 to 6 As shown, the piezoelectric MEMS microphone of this embodiment of the invention also includes a second piezoelectric unit 5 disposed on the diaphragm 2. The second piezoelectric unit 5 is coaxially disposed with the diaphragm 2, and the second piezoelectric unit 5 and the first piezoelectric stacked structure are both located on the same side of the diaphragm 2.

[0059] Having land, such as Figure 4 and Figure 5 As shown, in this embodiment of the invention, the second piezoelectric unit 5 is a regular octagon similar in shape to the diaphragm 2. The second piezoelectric unit 5 is located in the central region of the diaphragm 2, and its radial dimension is smaller than that of the diaphragm 2. Each side of the second piezoelectric unit 5 is parallel to each side of the diaphragm 2 structure. The radial dimension of the second piezoelectric unit 5 is 1 / 5 to 2 / 5 of the radial dimension of the diaphragm 2, in order to collect the strain state of the central region of the diaphragm 2. Both the second piezoelectric unit 5 and the first piezoelectric stack structure are located on the upper side of the diaphragm 2 and on the outer side of the cavity 10.

[0060] like Figure 5 and Figure 6 As shown, the second piezoelectric unit 5 of this embodiment includes a second piezoelectric thin film layer 51, a third electrode layer 52, and a fourth electrode layer 53 with the same radial dimensions. The third electrode layer 52 and the fourth electrode layer 53 are located on the upper and lower sides of the second piezoelectric thin film layer 51, respectively. The fourth electrode layer 53 is fixed to the surface of the diaphragm 2.

[0061] Through this configuration, the structural geometry of the second piezoelectric unit 5 and the diaphragm 2 is matched to achieve a coordinated stress field distribution. When sound pressure is applied to the diaphragm 2, the second piezoelectric unit 5, located in the central region of the diaphragm 2, has a rigid island structure, which in turn generates an inertial amplification effect on the diaphragm 2. This transforms the overall bending deformation into highly concentrated strain in the central region of the diaphragm 2, significantly increasing the charge output density per unit area of ​​the second piezoelectric unit 5, thereby further enhancing the overall sensitivity of the microphone.

[0062] The embodiments of the present invention also include a third pad 81 and a fourth pad 82, with the third electrode layer 52 electrically connected to the third pad 81 and the fourth electrode layer 53 electrically connected to the fourth pad 82. That is, the electrical signals collected by the second piezoelectric unit 5 and the first piezoelectric unit 4 are output independently of each other.

[0063] It should be noted that the other structures in the embodiments of the present invention are exactly the same as those in Embodiment 1. The second piezoelectric unit 5 has the same stacked structure as the first piezoelectric unit 4. The material selection for the stacked structure is the same as that in Embodiment 1, so it will not be described in detail here.

[0064] Example 3

[0065] like Figure 7 As shown, the difference from Embodiment 2 is that the second piezoelectric unit 5 in this embodiment is an annular frame 6 with a regular octagon, located at the edge region of the diaphragm 2. Each side of the diaphragm 2 structure is parallel to each side of the annular frame 6. The width of the annular frame 6 along the radial direction of the diaphragm 2 is 1 / 10 to 1 / 5 of the radial dimension of the diaphragm 2, and the annular frame 5 is located at the edge of the diaphragm 2, recessed inwards by 1 / 10 to 1 / 5 of the radial dimension of the diaphragm 2.

[0066] With this setup, on the one hand, by utilizing the maximum strain area at the edge of the diaphragm 2 during vibration, the second piezoelectric unit 5 can directly capture the edge strain with the highest vibration energy density to achieve efficient electromechanical conversion; on the other hand, by taking advantage of the small influence of air damping on edge vibration, noise interference is effectively reduced, thereby improving the signal-to-noise ratio characteristics of the microphone signal.

[0067] It should be noted that the other structures in the embodiments of the present invention are exactly the same as those in Embodiment 2, so they will not be described again here.

[0068] Example 4

[0069] The difference from the piezoelectric MEMS microphone in Embodiment 1 is that, in this embodiment of the invention, the two first piezoelectric units 4, which are symmetrically positioned in the radial direction of the radiating array, are divided into four differential pairs. Each differential pair is isolated from each other and the electrical signal of each differential pair is differentially amplified.

[0070] Specifically, such as Figure 2 As shown, the first electrode layer 42 and the second electrode layer 43 of each cantilever beam 3 independently output electrical signals. The eight cantilever beams 3 are numbered clockwise as v01, v02, v03, v04, v10, v20, v30, and v40, and divided into four differential pairs. In each differential pair, v0x and vx0 form a differential pair (e.g., v01-v10). The first electrode layer 42 and the second electrode layer 43 of each differential pair are independently connected to differential amplifiers. The electrical signals acquired by each differential pair are processed by differential amplifiers, and the signal channels of the four differential pairs are isolated from each other, realizing independent and synchronous electrical signal acquisition, which effectively ensures the sensitivity of the microphone to sound pressure acquisition.

[0071] Example 5

[0072] Based on the same inventive concept, the present invention also provides a preparation method of Example 1 or 4, comprising:

[0073] S1. A thin film layer is deposited on substrate 1 using plasma-enhanced chemical vapor deposition, and a regular n-sided diaphragm 2 and n radially distributed cantilever beams 3 are designed.

[0074] S2. Using selective deposition or patterning techniques, n corresponding first piezoelectric units 4 are deposited in the planned n cantilever beam 3 regions respectively;

[0075] S3. Use photolithography and metal deposition processes to etch the leads and pads that are electrically connected to the first piezoelectric unit 4;

[0076] S4. Using photolithography and deep reactive ion technology, a cavity 10 of a regular n-prism is etched on the back side of the substrate 1, which is coaxial with the diaphragm 2 and the cantilever beam 3. The diaphragm 2 and the n cantilever beams 3 are released to obtain a piezoelectric MEMS microphone.

[0077] Specifically, in step S1, an SOI silicon wafer or a single crystal silicon with an insulating layer is used as substrate 1, a silicon nitride or silicon oxide thin film layer is deposited on substrate 1, and an octagonal diaphragm 2 and eight radially distributed cantilever beams 3 are planned on the deposited thin film layer.

[0078] In step S2, a corresponding first piezoelectric unit 4 is deposited in each region of the cantilever beam 3 using selective vapor deposition. Specifically, a second electrode layer 43 is deposited in the region of the cantilever beam 3, with the deposition material being molybdenum, gold, or aluminum; then a first piezoelectric thin film layer 41 is deposited, with the deposition material being aluminum nitride or lead zirconate titanate; finally, a first electrode layer 42 is deposited, with the deposition material being gold, aluminum, or chromium.

[0079] It should be noted that by using a shadow mask or selective etching process, the width of the first electrode layer 42 after deposition is precisely controlled to be 70% ± 5% of the width of the second electrode layer 43, and it is symmetrically distributed in the width direction of the cantilever beam 3.

[0080] In addition, a passivation layer, such as a SiO2 layer, is deposited in the exposed portion of the first electrode layer 42 and the second electrode layer 43 using a plasma-enhanced chemical vapor deposition process to protect the electrode layers from oxidation; then, a connection hole for leading out the electrode layer signal is formed in a portion of the passivation layer through etching.

[0081] In step S3, lead wires and pads are etched using photolithography and metal deposition processes, and the first electrode layer 42 and the second electrode layer 43 are connected to the first pad 71 and the second pad 72 respectively via lead wires to facilitate connection to external circuits.

[0082] It should be noted that the layout and connection method of the etched leads are based on the connection method of the first piezoelectric unit 4 in Embodiment 1 or Embodiment 4.

[0083] In step S4, a regular n-prism cavity 10 penetrating the substrate 1 is etched from one side of the back side of the substrate 1. That is, the diaphragm 2 and the eight cantilever beams 3 structure are released from one side of the cavity 10 of the substrate 1 to obtain a piezoelectric MEMS microphone.

[0084] Finally, the mass-produced piezoelectric MEMS microphones are placed in an annealing furnace for annealing treatment to eliminate residual stress in the microphones, avoid structural cracking between the diaphragm and the cantilever beam, and improve the quality and lifespan of the microphones.

[0085] The annealing temperature is 350℃-450℃, and the annealing time is 30min-180min.

[0086] Example 6

[0087] The present invention also provides preparation methods of Example 2 or Example 3, which differ from the preparation method of Example 5 in that the preparation method of this example further includes, in step S2, selective deposition or patterning process to simultaneously deposit the second piezoelectric unit 5 on the diaphragm 2.

[0088] Among them, the patterning process selects two types of templates for deposition shape. One is a regular octagonal structure, in which the second piezoelectric unit 5 is deposited and arranged in an island-like manner on the central region of the diaphragm 2, thereby preparing the second piezoelectric unit 5 structure in Example 2; the other is a regular octagonal ring frame 6 structure, in which the second piezoelectric unit 5 is deposited and arranged at the edge region of the diaphragm 2, thereby preparing the second piezoelectric unit 5 structure in Example 3.

[0089] In step S3, electrode interconnects are formed by photolithography and metal deposition processes, and the third electrode layer 52 and the fourth electrode layer 53 of the second piezoelectric unit 5 are connected to the third pad 81 and the fourth pad 82 respectively by leads to facilitate connection to external circuits.

[0090] It should be noted that the connection lines of the first piezoelectric unit 4 and the second piezoelectric unit 5 are completely independent of each other.

[0091] It should be noted that the other steps in this embodiment are exactly the same as those in Embodiment 5, and therefore will not be repeated here.

[0092] Example 7

[0093] Based on the same inventive concept, the present invention also provides an electronic device, including any one of the piezoelectric MEMS microphones in embodiments 1-4.

[0094] The above are merely embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of the claims of the present invention pending approval.

Claims

1. A piezoelectric MEMS microphone, characterized in that, include: A substrate (1) having a cavity (10) extending through the thickness direction, the cavity (10) being a regular n-prism; The diaphragm (2) is a regular n-sided polygon, and the diaphragm (2) is coaxially arranged with the substrate (1) and located on one side of the cavity (10); n cantilever beams (3) are arranged in a radial array. One end of each cantilever beam (3) is connected to the corresponding vertex position of the diaphragm (2), and the other end of each cantilever beam (3) is connected to the middle position of the corresponding edge line of the opening end of the cavity (10). n first piezoelectric units (4) are respectively corresponding to and fixed on n cantilever beams (3); Wherein, n is an even number not less than 6. When the sound pressure drives the diaphragm (2) to vibrate and displace along the thickness direction of the substrate (1), causing the cantilever beam (3) to generate strain, the first piezoelectric unit (4) located on the cantilever beam (3) generates an electrical signal through the piezoelectric effect.

2. The piezoelectric MEMS microphone according to claim 1, characterized in that, The diaphragm (2) is integrally formed with the cantilever beam (3).

3. The piezoelectric MEMS microphone according to claim 1, characterized in that, The diaphragm (2) and the cantilever beam (3) are both located at the opening end of the cavity (10), and the first piezoelectric unit (4) is disposed away from the cavity (10).

4. The piezoelectric MEMS microphone according to claim 1, characterized in that, It also includes a second piezoelectric unit (5) disposed on the diaphragm (2), the second piezoelectric unit (5) being coaxially disposed with the diaphragm (2), and the second piezoelectric unit (5) and the first piezoelectric stack structure being located on the same side of the diaphragm (2).

5. The piezoelectric MEMS microphone according to claim 4, characterized in that, The second piezoelectric unit (5) is a regular n-sided polygon similar in shape to the diaphragm (2). The second piezoelectric unit (5) is located in the central region of the diaphragm (2). The radial dimension of the second piezoelectric unit (5) is smaller than the radial dimension of the diaphragm (2).

6. The piezoelectric MEMS microphone according to claim 5, characterized in that, The radial dimension of the second piezoelectric unit (5) is 1 / 5 to 2 / 5 of the radial dimension of the diaphragm (2).

7. The piezoelectric MEMS microphone according to claim 4, characterized in that, The second piezoelectric unit (5) is an annular frame (5) with a regular n-sided shape, and the annular frame (5) is located in the edge region of the diaphragm (2).

8. The piezoelectric MEMS microphone according to claim 7, characterized in that, Along the radial direction of the diaphragm (2), the width of the annular frame (5) is 1 / 10-1 / 5 of the radial dimension of the diaphragm (2), and the annular frame (5) is located at the edge of the diaphragm (2) and recessed inward by 1 / 10-1 / 5 of the radial dimension of the diaphragm (2).

9. The piezoelectric MEMS microphone according to claim 1, characterized in that, The length direction of the first piezoelectric unit (4) is consistent with the radiation direction of the cantilever beam (3). The first piezoelectric unit (4) includes a first piezoelectric thin film layer (41) and a first electrode layer (42) and a second electrode layer (43) located on both sides of the first piezoelectric thin film layer (41). The second electrode layer (43) is fixed at the middle position in the width direction of the cantilever beam (3). The width of the first piezoelectric thin film layer (41) is the same as the width of the second electrode layer (43). The width of the first electrode layer (42) is 70% ± 5% of the width of the second electrode layer (43).

10. The piezoelectric MEMS microphone according to claim 9, characterized in that, n first electrode layers (42) are connected in parallel to output electrical signals, and n second electrode layers (43) are integrally formed and connected in parallel to output electrical signals.

11. The piezoelectric MEMS microphone according to claim 1, characterized in that, When n is even, the two first piezoelectric units (4) that are symmetrical to each other in the radial direction of the radiation array are divided into n / 2 differential pairs. Each differential pair is isolated from each other and the electrical signal collected by each differential pair is differentially amplified.

12. The piezoelectric MEMS microphone according to claim 9, characterized in that, The material of the first piezoelectric thin film layer (41) includes any one of aluminum nitride, zinc oxide, and lead zirconate titanate; and / or The materials of the first electrode layer (42) and the second electrode layer (43) include any one of molybdenum, gold, aluminum and chromium.

13. The piezoelectric MEMS microphone according to claim 1, characterized in that, The diaphragm (2) material includes silicon nitride or silicon oxide; and / or The cantilever beam (3) is made of silicon nitride or silicon oxide; and / or The substrate (1) material includes silicon oxide or monocrystalline silicon.

14. A method for fabricating a piezoelectric MEMS microphone according to any one of claims 1-13, characterized in that, include: S1. A thin film layer is deposited on a substrate (1) using plasma-enhanced chemical vapor deposition and a regular n-sided diaphragm (2) and n radially distributed cantilever beams (3) are planned. S2. Using selective deposition or patterning processes, n corresponding first piezoelectric units (4) are deposited in the planned n cantilever beam (3) regions respectively; S3. Use photolithography and metal deposition processes to etch the leads and pads that are electrically connected to the first piezoelectric unit (4); S4. Using photolithography and deep reactive ion technology, a cavity (10) of a regular n-prism is etched on the back side of the substrate (1) and is coaxially arranged with the diaphragm (2) and the cantilever beam (3). The diaphragm (2) and the n cantilever beams (3) are released to obtain a piezoelectric MEMS microphone.

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