Composite beam microphone

Abstract

The invention provides a composite beam microphone, and belongs to the field of piezoelectric microphones, the composite beam microphone comprises a substrate, the upper surface of the substrate is provided with a circular groove, the interior of the substrate is provided with a cavity, and the cavity is located right below the groove; the central vibrating diaphragm is arranged in the groove and is located at the circle center of the groove; the transition beams are arranged around the central diaphragm at intervals and are connected to the central diaphragm, and a first gap is reserved between every two adjacent transition beams; the clamped beams are arranged around the central diaphragm at intervals, and the two ends of the clamped beams in the radial direction of the groove are connected to the inner wall of the groove and the transition beams respectively; the cantilever beams are arranged between the adjacent clamped beams and connected to the transition beams, and second gaps are reserved between the cantilever beams and the inner walls of the grooves and between the cantilever beams and the clamped beams. By changing the structural form of the inner beam of the microphone, increasing the number of clamped beams and the combination form between the beams, increasing the area of a high stress concentration area and combining the reasonable layout of the central diaphragm, the transition beams, the clamped beams and the cantilever beams, the stress distribution is more uniform, and the effective utilization rate of the diaphragm area is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of piezoelectric microphones, and in particular to a combined beam microphone. Background Art

[0002] A microphone is a device that converts sound signals into electrical signals. It is widely used in microphones, mobile phones, PCs, and in-vehicle voice recognition devices. After a long period of development, the performance indicators of microphones are now more focused on intelligence, digitization, and miniaturization. Today, MEMS piezoelectric microphone technology is increasingly integrated with aerospace, biomedicine, consumer electronics, information communications, and military industries, which places higher demands on the reliability and sensitivity of microphones. At present, capacitive microphones occupy the main market share, but piezoelectric microphones will be widely used in the field of aeroacoustics in the future due to their durability, high sensitivity, low noise, and no need for external power drive.

[0003] In the structure of a traditional beam-type piezoelectric microphone, the fixed end of the beam is set at the periphery or center of the vibration area. For example, in the piezoelectric MEMS microphone disclosed in Chinese patent CN115278490A, two cantilever beams are cross-set to form a fixed boundary, resulting in only one high stress concentration area on a single beam, which is located near the fixed boundary, resulting in a small effective area of ​​the piezoelectric film and a small microphone output. Therefore, it is necessary to improve the structure of the cantilever beam to increase the effective area of ​​the film and improve the performance of the microphone. Summary of the invention

[0004] In view of this, the present invention proposes a combined beam microphone to solve the problem that current piezoelectric microphones usually have only one high stress concentration area on a single beam, resulting in a small effective area of ​​the piezoelectric film and a smaller microphone output.

[0005] The technical solution of the present invention is implemented as follows: the present invention provides a combined beam microphone, including a substrate, a circular groove is provided on the upper surface of the substrate and a cavity is provided inside the substrate, and the cavity is located directly below the groove; a central diaphragm is arranged in the groove and located at the center of the groove; a plurality of transition beams are arranged at intervals around the central diaphragm and connected to the central diaphragm, and a first gap is left between adjacent transition beams; a plurality of fixed support beams are arranged at intervals around the central diaphragm, and the two ends of the fixed support beams along the radial direction of the groove are respectively connected to the inner wall of the groove and the transition beam; a cantilever beam is arranged between adjacent fixed support beams and connected to the transition beam, and a second gap is left between the cantilever beam and the inner wall of the groove and the fixed support beam.

[0006] On the basis of the above technical scheme, preferably, the central diaphragm, transition beam, fixed support beam and cantilever beam are all made of piezoelectric thin film materials and constitute a piezoelectric layer, and the top electrode and the bottom electrode are respectively provided on the upper surface and the lower surface of the piezoelectric layer to form a piezoelectric stack structure; the substrate includes a device layer and a release layer, the piezoelectric stack structure is arranged on the device layer, and the release layer is arranged below the device layer and around the cavity.

[0007] More preferably, the surface of the piezoelectric layer is provided with an electrode area for laying electrodes, and the electrode areas located on the central diaphragm, the transition beam, the clamped beam and the cantilever beam are isolated and arranged.

[0008] More preferably, the composite beam microphone has an axisymmetric structure with the center of the central diaphragm, and the overall structure is equally divided into four quadrants, and the structure of each quadrant is consistent.

[0009] More preferably, each quadrant includes a transition beam, two fixed-support beams and a cantilever beam; the two fixed-support beams are symmetrically arranged on both sides of the cantilever beam; and a first gap is left between adjacent fixed-support beams in adjacent quadrants.

[0010] More preferably, the transition beam, the clamped beam and the cantilever beam are all fan-shaped.

[0011] More preferably, the radius of the piezoelectric layer is r1, the sum of the radii of the center diaphragm and the transition beam is r2, and the radius of the center diaphragm is r3, satisfying r2=r1×k1 and r3=r2×k2, where k1 and k2 are proportional coefficients and have a value range of 0 to 1.

[0012] More preferably, the output of the electrode area of ​​the piezoelectric layer increases with the increase of k1, and decreases with the increase of k2; the device characteristic frequency of the composite beam microphone increases with the increase of k1, and increases with the increase of k2.

[0013] More preferably, a third gap is opened on the device layer, and the third gap is connected between the second gap and the cavity.

[0014] More preferably, the substrate is a SOI wafer substrate or a thermal oxide sheet, and the piezoelectric film material is one of aluminum nitride, scandium-doped aluminum nitride, PZT, PVDF, LiNbO3, LiTaO3 and PMN-PT.

[0015] The combined beam microphone of the present invention has the following beneficial effects compared with the prior art:

[0016] (1) The present invention increases the area of ​​high stress concentration by changing the structural form of the internal beam of the microphone, increasing the number of fixed-support beams and the combination form of the beams, thereby increasing the effective utilization rate of the diaphragm area and improving the sensitivity of the microphone; at the same time, combined with the reasonable layout of the central diaphragm, transition beam, fixed-support beam and cantilever beam, the stress distribution is more uniform, and the microphone can maintain a high structural stability and reliability.

[0017] (2) The present invention can flexibly adjust the characteristic frequency of the microphone to meet different sound collection requirements by adjusting two proportional coefficients. As k1 increases, the characteristic frequency of the device increases, which is suitable for high-frequency sound collection; and as k2 increases, the frequency response is further adjusted to meet the use requirements in different scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A top view of a quarter structure of a composite beam microphone of the present invention;

[0020] Figure 2 A top view of a quarter structure of another embodiment of a composite beam microphone of the present invention;

[0021] Figure 3 A cross-sectional view of a quarter structure of the composite beam microphone of the present invention;

[0022] Figure 4 A three-dimensional diagram of a quarter structure of another embodiment of a composite beam microphone of the present invention;

[0023] Figure 5 It is a simulation relationship diagram of the proportional coefficients k1 and k2 of the present invention and the characteristic frequency and output voltage of the device;

[0024] Figure 6 1 and 1 are simulated stress diagrams of a comparative structure and a structure of the present invention, wherein a is the comparative structure and b is the structure of the present invention.

[0025] In the figure: 1. substrate; 11. device layer; 12. release layer; 101. groove; 102. cavity; 103. third gap; 2. central diaphragm; 3. transition beam; 301. first gap; 4. fixed beam; 5. cantilever beam; 501. second gap; 6. piezoelectric layer; 61. top electrode; 62. bottom electrode. DETAILED DESCRIPTION

[0026] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] like Figure 1 As shown, combined Figure 4 A composite beam microphone of the present invention comprises a substrate 1, a central diaphragm 2, a transition beam 3, a fixed support beam 4 and a cantilever beam 5.

[0028] The upper surface of the substrate 1 is provided with a circular groove 101 and a cavity 102 is provided inside, and the cavity 102 is located directly below the groove 101. The substrate 1 is the basic supporting structure of the entire microphone, which plays the role of supporting and isolating various components. The role of the cavity 102 is to reduce the interference of external noise on the performance of the microphone and ensure more accurate collection of audio signals. The position and structural setting of the cavity 102 can effectively enhance the frequency response range and sensitivity of the microphone.

[0029] The center diaphragm 2 is disposed in the groove 101 and is located at the center of the groove 101. The center diaphragm 2 is the core part of the microphone, which directly responds to sound fluctuations and converts them into electrical signals. The design of the center diaphragm 2 optimizes the frequency response characteristics through its material, thickness, shape and other parameters, and further improves the signal collection effect by connecting to the transition beam 3.

[0030] A plurality of transition beams 3 are arranged around the central diaphragm 2 at intervals and connected to the central diaphragm 2, and a first gap 301 is left between adjacent transition beams 3. The function of the transition beam is to effectively transmit the sound fluctuations captured by the diaphragm to the fixed support beam 4 and the cantilever beam 5, and to control the movement of the diaphragm. The first gap 301 between the transition beam and the adjacent beam is ingeniously designed to ensure the stability and accuracy of signal transmission.

[0031] A plurality of fixing beams 4 are arranged at intervals around the center diaphragm 2, and the two ends of the fixing beams 4 along the radial direction of the groove 101 are respectively connected to the inner wall of the groove 101 and the transition beam 3. The fixing beams 4 are located outside the transition beam 3, and their existence provides the necessary support force for the center diaphragm 2 to prevent the center diaphragm 2 from excessive deformation, while also ensuring the accurate conduction of the audio signal. The layout and design of the fixing beams 4 have a direct impact on the frequency response, sensitivity and other performance of the microphone.

[0032] The cantilever beam 5 is arranged between adjacent fixed beams 4 and connected to the transition beam 3, and a second gap 501 is left between the cantilever beam 5 and the inner wall of the groove 101 and the fixed beam 4. The cantilever beam 5 plays a role in further enhancing the conduction of audio signals and vibration regulation. The design of the second gap 501 between the cantilever beam 5 and the fixed beam 4 can effectively suppress unnecessary resonance and optimize signal transmission.

[0033] In this embodiment, different electrical polarization designs can be performed on the device according to different requirements, such as Figure 1 As shown, the electrode area is divided by dotted lines according to the fixed support beam 4, cantilever beam 5, transition beam 3 and central diaphragm 2, and different electrical connection and extraction methods are performed, such as full series connection, full parallel connection or series-parallel combination. The electrode covers the entire fan-shaped beam, the capacitance is large, and the introduced capacitance noise is large. The electrode coverage area can be optimized to cover only the high stress area to obtain a larger output response and introduce less noise, thereby improving the device signal-to-noise ratio.

[0034] exist Figure 3 In a preferred embodiment shown, the central diaphragm 2, the transition beam 3, the fixed support beam 4 and the cantilever beam 5 are all made of piezoelectric film materials and form a piezoelectric layer 6. The upper surface and the lower surface of the piezoelectric layer 6 are respectively provided with a top electrode 61 and a bottom electrode 62 to form a piezoelectric stack structure of a single crystal; or the piezoelectric stack structure can also be made of a bottom electrode 62, a piezoelectric layer 6, a middle electrode, another piezoelectric layer 6 and a top electrode 61 from bottom to top, thereby forming a piezoelectric stack structure of a double crystal. The piezoelectric stack structure can be set with different polarization modes, and the outer side of the substrate 1 is respectively provided with lead-out electrodes for extracting electrode electrical signals. An insulating layer is provided between the lead-out electrodes of different electrode layers. The bottom electrode 62, the middle electrode and the top electrode 61 can be electrically connected in full series, full parallel or a combination of series and parallel.

[0035] The substrate 1 includes a device layer 11 and a release layer 12. A piezoelectric stacked structure is arranged on the device layer 11. The release layer 12 is arranged below the device layer 11 and surrounds the cavity 102. In the production process of the microphone through the MEMS process, the release layer 12 is used as a temporary support layer to help maintain the position and shape of other structures (such as diaphragms, beams, etc.) to prevent deformation or instability in subsequent process steps; especially in micro-machining or thin film deposition technology, the release layer 12 is usually temporary, and the purpose is to be removed (i.e., "released") after completing other processes of the device. By removing the release layer 12, structures such as diaphragms and beams can be allowed to move or vibrate freely, thereby realizing the sensing function of the microphone.

[0036] exist Figure 1In a preferred embodiment shown, an electrode area for laying electrodes is provided on the surface of the piezoelectric layer 6, and the electrode areas on the central diaphragm 2, the transition beam 3, the clamping beam 4 and the cantilever beam 5 are isolated and arranged. This electrode distribution design not only ensures the signal transmission efficiency, but also avoids the generation of signal interference and current noise.

[0037] exist Figure 2 In a preferred embodiment shown, the composite beam microphone is axially symmetrical with the center of the central diaphragm 2, and the overall structure is equally divided into four quadrants, each quadrant having the same structure. Ideally, more quadrants can be used, but four quadrants are preferred.

[0038] exist Figure 2 In a preferred embodiment shown in the figure, each quadrant includes a transition beam 3, two fixed beams 4 and a cantilever beam 5; the two fixed beams 4 are symmetrically arranged on both sides of the cantilever beam 5; a first gap 301 is left between adjacent fixed beams 4 in adjacent quadrants. Based on the design of this embodiment, refer to Figure 6 , provides a contrasting structure, e.g. Figure 6 (a). Compared with this embodiment ( Figure 6 Compared with the comparative structure shown in (b), although the comparative structure also has a fixed support beam 4 and a cantilever beam 5, the two are directly connected to the central diaphragm 2 without passing through the transition beam 3. The structure of this embodiment has a transition beam 3 compared with the comparative structure, which further increases the effective utilization area of ​​the membrane. After simulating the stress of the above two structures, it is obtained Figure 6 From the simulated stress diagram shown, it can be found that the high stress concentration area of ​​the structure of this embodiment is uniform and larger in area, and for the dual-chip, the characteristic frequency will not drop into the audible sound range.

[0039] exist Figure 2 In a preferred embodiment shown, the transition beam 3, the fixed support beam 4 and the cantilever beam 5 are all fan-shaped with arc-shaped boundaries; the three form a whole fan-shaped beam structure, and the electrode can cover the whole fan-shaped beam.

[0040] exist Figure 5 In a preferred embodiment shown in the figure, the radius of the piezoelectric layer 6 is r1, the sum of the radii of the central diaphragm 2 and the transition beam 3 is r2, and the radius of the central diaphragm 2 is r3. The multi-physics numerical analysis software Comsol Multiphysics is used to perform parameter scanning to obtain Figure 5 The relationship between the proportional coefficient and the device characteristic frequency and output voltage satisfies r2=r1×k1 and r3=r2×k2, where k1 and k2 are proportional coefficients and have a value range of 0 to 1.

[0041] exist Figure 5In a preferred embodiment shown, under the condition of fixed device size and electrical connection, the output of the electrode area of ​​the piezoelectric layer 6 increases with the increase of k1 and decreases with the increase of k2; the device characteristic frequency of the composite beam microphone increases with the increase of k1 and increases with the increase of k2. Under the above rules, different proportional coefficients can be selected according to different demand directions such as high frequency or low frequency.

[0042] exist Figure 4 In a preferred embodiment shown, a third gap 103 is provided on the device layer 11, and the third gap 103 communicates between the second gap 501 and the cavity 102. The third gap 103 effectively improves the dynamic response and stability of the microphone, while helping to avoid interference from air fluctuations.

[0043] exist Figure 1 In a preferred embodiment shown, a piezoelectric microphone is a sensor based on the piezoelectric effect, which can convert sound wave signals into electrical signals. Therefore, when designing and manufacturing a piezoelectric microphone, it is very important to select a suitable substrate and piezoelectric material. In this embodiment, substrate 1 is an SOI wafer substrate or a thermal oxide wafer. SOI wafers have good mechanical properties and electrical insulation, and are suitable for the application of micro-electromechanical systems (MEMS). They can also effectively isolate electrical signals, reduce noise interference, and improve the sensitivity and signal-to-noise ratio of microphones. Thermally oxidized silicon wafers are usually used to manufacture high-quality piezoelectric films, which can provide excellent interface quality. Their good thermal stability and mechanical strength make them an ideal choice for piezoelectric devices. The piezoelectric film material is one of aluminum nitride, scandium-doped aluminum nitride, PZT, PVDF, LiNbO3, LiTaO3 and PMN-PT. Aluminum nitride is a wide bandgap semiconductor material with good piezoelectric properties and thermal stability. Scandium-doped aluminum nitride is a derivative material of aluminum nitride. Its piezoelectric properties are improved by doping scandium elements, and it has a higher piezoelectric constant. Lead zirconate titanate (PZT) is one of the most commonly used piezoelectric materials with a high piezoelectric constant and good mechanical strength. It is suitable for low-frequency and high-frequency acoustic applications, but it is highly sensitive to temperature and humidity. Polyvinylidene fluoride (PVDF) is a polymer material with good flexibility and a high piezoelectric constant. Lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) have excellent piezoelectric and photoelectric properties and are suitable for high-frequency and optoelectronic integration applications. Due to their excellent temperature stability, they are often used in high-precision sensors. PMN-PT (lead magnesium titanate) is a new type of piezoelectric material with extremely high piezoelectric properties and sensitivity. It is suitable for high-precision and high-sensitivity sensors, but its manufacturing cost is relatively high. The piezoelectric microphone of this embodiment is prepared using MEMS technology.

[0044] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A composite beam microphone, characterized in that: include: A substrate (1) having a circular groove (101) on its upper surface and a cavity (102) inside thereof, wherein the cavity (102) is located directly below the groove (101); A central diaphragm (2) is arranged in the groove (101) and is located at the center of the groove (101); A plurality of transition beams (3) are arranged at intervals around the central diaphragm (2) and connected to the central diaphragm (2), with a first gap (301) being left between adjacent transition beams (3); A plurality of fixed support beams (4) are arranged at intervals around the central diaphragm (2), and two ends of the fixed support beams (4) along the radial direction of the groove (101) are respectively connected to the inner wall of the groove (101) and the transition beam (3); A cantilever beam (5) is arranged between adjacent fixed support beams (4) and connected to the transition beam (3); a second gap (501) is left between the cantilever beam (5), the inner wall of the groove (101) and the fixed support beam (4).

2. A combined beam microphone according to claim 1, characterized in that: include: The central diaphragm (2), transition beam (3), fixed support beam (4) and cantilever beam (5) are all made of piezoelectric film material and form a piezoelectric layer (6); the upper surface and lower surface of the piezoelectric layer (6) are respectively provided with a top electrode (61) and a bottom electrode (62) to form a piezoelectric stacked structure; The substrate (1) comprises a device layer (11) and a release layer (12); a piezoelectric stack structure is arranged on the device layer (11); and the release layer (12) is arranged below the device layer (11) and surrounds the cavity (102).

3. A composite beam microphone according to claim 2, characterized in that: include: The surface of the piezoelectric layer (6) is provided with an electrode area for laying electrodes, and the electrode areas located on the central diaphragm (2), the transition beam (3), the fixed support beam (4) and the cantilever beam (5) are arranged in isolation.

4. The combined beam microphone according to claim 2, characterized in that: The combined beam microphone is an axisymmetric structure with the center of the central diaphragm (2) in the form of an axis, and the overall structure is equally divided into four quadrants, each quadrant having a consistent structure.

5. The combined beam microphone according to claim 4, characterized in that: Each quadrant comprises a transition beam (3), two fixed support beams (4) and a cantilever beam (5); the two fixed support beams (4) are symmetrically arranged on both sides of the cantilever beam (5); and a first gap (301) is left between adjacent fixed support beams (4) in adjacent quadrants.

6. The combined beam microphone according to claim 5, characterized in that: The transition beam (3), the fixed support beam (4) and the cantilever beam (5) are all fan-shaped.

7. The combined beam microphone according to claim 6, characterized in that: The radius of the piezoelectric layer (6) is r1, the sum of the radii of the central diaphragm (2) and the transition beam (3) is r2, and the radius of the central diaphragm (2) is r3, satisfying r2=r1×k1 and r3=r2×k2, wherein k1 and k2 are proportional coefficients and have a value range of 0 to 1.

8. The combined beam microphone according to claim 7, characterized in that: The output of the electrode area of ​​the piezoelectric layer (6) increases as k1 increases, and decreases as k2 increases; the device characteristic frequency of the combined beam microphone increases as k1 increases, and increases as k2 increases.

9. The combined beam microphone according to claim 6, characterized in that: A third gap (103) is provided on the device layer (11), and the third gap (103) is connected between the second gap (501) and the cavity (102).

10. The combined beam microphone according to claim 2, characterized in that: The substrate (1) is an SOI wafer substrate or a thermal oxide film, and the piezoelectric film material is one of aluminum nitride, scandium-doped aluminum nitride, PZT, PVDF, LiNbO3, LiTaO3 and PMN-PT.

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