MEMS

Abstract

The present invention provides a micro-electromechanical system, which includes: a housing defining a cavity and an opening communicating with the cavity; a diaphragm mounted at the opening; at least one cantilever located in the cavity, the cantilever including a first end, a second end and a fulcrum located between the first end and the second end; a plunger located between the diaphragm and the cantilever and used to transmit the displacement of the diaphragm to the first end of the cantilever; and a sensor element connected to the second end of the cantilever; wherein the distance between the first end and the fulcrum is less than the distance between the second end and the fulcrum. The micro-electromechanical system of the present invention has the advantages of high signal-to-noise ratio, small packaging volume, high sensitivity, etc. The stiffness of the diaphragm of the present invention is an order of magnitude higher than that of the diaphragm of the related art, avoiding mechanical collapse and large DC deformation under 1 standard atmosphere (atm).

Description

Technical Field

[0001] The present invention relates to the field of electroacoustic transducers, and in particular to a micro-electromechanical system. Background Art

[0002] Conventional micro-electromechanical system (MEMS) microphones typically include a back volume behind the diaphragm. The back volume is a semi-sealed volume of air that undergoes compression and expansion when there is an input sound wave. For a limited package size, the back volume is necessary to allow the diaphragm to move under the action of external pressure waves. However, the back volume is currently the largest source of acoustic noise, which reduces the signal-to-noise ratio (SNR) of the microphone. The smaller the back volume, the higher the acoustic noise generated by the back volume. Therefore, it is very difficult to have a microphone with a signal-to-noise ratio greater than about 74 dB unless the package size is very large. However, for mobile electronic devices, very large package sizes are not feasible.

[0003] An effective way to achieve very high signal-to-noise ratio in a normal or smaller size package is to make the back volume a vacuum. This type of vacuum back volume microphone presents a significant challenge. The pressure difference of standard atmosphere (1atm) between air and vacuum will break a normal diaphragm. Therefore, a diaphragm with higher stiffness is required. However, a high stiffness diaphragm will result in low sensitivity. Conventional sensing designs will not work.

[0004] Therefore, we hope to provide an improved MEMS that can at least partially solve the above problems. Summary of the invention

[0005] In view of this, an embodiment of the present invention provides a micro-electromechanical system, which includes: a housing defining a cavity and an opening connected to the cavity; a diaphragm installed at the opening; at least one cantilever located in the cavity, the cantilever including a first end, a second end and a fulcrum located between the first end and the second end; a plunger located between the diaphragm and the cantilever to transfer the displacement of the diaphragm to the first end of the cantilever; and a sensor element connected to the second end of the cantilever; wherein the distance between the first end and the fulcrum is smaller than the distance between the second end and the fulcrum.

[0006] In one embodiment, the cavity is hermetically sealed, and the internal pressure of the cavity is less than the external atmospheric pressure.

[0007] In one embodiment, the cavity is evacuated.

[0008] In one embodiment, the sensing element includes a fixed part fixed relative to the housing and a movable part connected to the second end of the cantilever and movable relative to the fixed part.

[0009] In one embodiment, the movable component includes a plurality of conductive movable fingers, and a first gap is formed between every two adjacent movable fingers; the fixed component includes a plurality of conductive fixed fingers, and a second gap is formed between every two adjacent fixed fingers; the plurality of movable fingers are respectively aligned with the plurality of second gaps of the fixed components, and the plurality of fixed fingers are respectively aligned with the plurality of first gaps of the movable component.

[0010] In one embodiment, the cantilever comprises a plurality of triangular or fan-shaped cantilever arms arranged in a circular array.

[0011] In one embodiment, the cantilever comprises a pair of rectangular cantilevers arranged in a linear array.

[0012] In one embodiment, the cantilever further includes at least one rib disposed at a surface thereof.

[0013] In one embodiment, the micro-electromechanical system further includes a support member disposed between the fulcrum and the housing.

[0014] In one embodiment, the size of the opening is smaller than the size of the cavity.

[0015] In one embodiment, the cantilever comprises a plurality of cantilevers connected in series.

[0016] In one embodiment, the multi-stage cantilever includes a first-stage cantilever, a second-stage cantilever and a third-stage cantilever, wherein the first end of the first-stage cantilever is connected to a first plunger, the second end of the first-stage cantilever is connected to the first end of the second-stage cantilever through a second plunger, the second end of the second-stage cantilever is connected to the first end of the third-stage cantilever through a third plunger, and the sensing element is connected to the second end of the third-stage cantilever.

[0017] In one embodiment, the first-stage cantilever, the second-stage cantilever and the third-stage cantilever each include a fulcrum located between the first end and the second end thereof, and a support member disposed between the fulcrum and the housing.

[0018] In one embodiment, the first end includes a curved portion having a low thickness.

[0019] In one embodiment, the first end includes a bend having one or more slits.

[0020] In embodiments of the present invention, the MEMS has the advantages of high signal-to-noise ratio, small package volume, and normal or high sensitivity. By increasing the mechanical sensitivity, it is easier to achieve the standard (-38 dB V / Pa) or higher total sensor sensitivity required for vacuum back cavity volume design. By making the cavity / back cavity volume a vacuum, it does not need to be larger than the conventional front volume and can be much smaller than the conventional front volume. This increases the possibility of using a higher signal-to-noise ratio microphone in a smaller package size than traditionally used, which is very attractive for all microphone applications, especially mobile applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] 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 embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0022] Figure 1 is a cross-sectional view of a micro-electromechanical system according to a first embodiment of the present invention;

[0023] Figure 2 is a schematic diagram of a cantilever of a micro-electromechanical system according to a first embodiment of the present invention;

[0024] Figure 3 is a schematic diagram of a cantilever of a micro-electromechanical system according to a second embodiment of the present invention;

[0025] Figure 4 and Figure 1 Similar, but showing the cross-section of the MEMS when the ambient pressure is negative;

[0026] Figure 5 and Figure 1 Similar, but showing the cross-section of the MEMS when the ambient pressure is positive;

[0027] Figure 6 and Figure 7 It is the working principle diagram of the cantilever of the MEMS;

[0028] Figure 8 and Fig. 9 is a cross-sectional view of a micro-electromechanical system according to a third embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the drawings in 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.

[0030] See also Figure 1 and Figure 2 The micro-electromechanical system 10 includes a housing 20 having a cavity 22 and an opening 24 communicating with the cavity 22 , a diaphragm 30 mounted at the opening 24 , at least one cantilever 40 located in the cavity 22 , and a plunger 50 located between the diaphragm 30 and the cantilever 40 .

[0031] In some embodiments, the cavity 22 surrounded by the housing 20 and the diaphragm 30 is sealed from the external atmosphere and vacuum. Alternatively, the pressure in the cavity 22 can be lower than the atmospheric pressure, such as 0.1 times the atmospheric pressure.

[0032] Each cantilever 40 includes a first end 42, a second end 44 and a fulcrum 46 located between the first end 42 and the second end 44. The cantilever 40 is provided with one or more ribs 48 on the surface facing the diaphragm 30 or opposite to the diaphragm 30, and the ribs 48 are used to increase the rigidity of the cantilever 40. A support member 49 is provided between the fulcrum 46 and the housing 20 so that the cantilever 40 can pivot around the fulcrum 46. The distance between the second end 44 and the fulcrum 46 is greater than the distance between the first end 42 and the fulcrum 46. In some embodiments, the distance between the second end 44 and the fulcrum 46 is greater than or equal to 10 times the distance between the first end 42 and the fulcrum 46. The hinge cantilever 40 is provided with a bent portion 47 at its first end 42. The bent portion 47 is formed by forming a cutout / groove / slit in the bent portion to reduce the rigidity of the bent portion, which is conducive to the bending of the cantilever 40 at the bent portion 47.

[0033] The first end 42 is connected to the plunger 50 . The plunger 50 is configured to transmit the displacement of the diaphragm 30 to the first end 42 of the cantilever 40 .

[0034] In some embodiments, the housing 20 is cylindrical or polygonal, and the plurality of cantilevers 40 are arranged in a circular array. Each cantilever 40 is triangular or fan-shaped. The first end 42 is located at the center of the circular array of cantilevers 40, and the second end 44 is located at the edge of the circular array of cantilevers 40. The plurality of cantilevers 40 may be formed separately and arranged in a circular array, with a gap formed between every two adjacent cantilevers 40; or, the plurality of cantilevers 40 are formed as a whole, with a gap formed between every two adjacent cantilevers 40.

[0035] The micro-electromechanical system 10 also includes a sensor element 60. The sensor element 60 includes a moving part 62 connected to the second end 44 of the cantilever 40 and a fixed part 64 connected to the housing 20. The moving part 62 includes a plurality of spaced-apart movable fingers 622 with first gaps 624 between the plurality of movable fingers 622, and the fixed part 64 includes a plurality of spaced-apart fixed fingers 642 with second gaps 644 between the plurality of fixed fingers 642. The plurality of movable fingers 622 are respectively aligned with the plurality of second gaps 644 of the fixed part 64, and the plurality of fixed fingers 642 are respectively aligned with the plurality of first gaps 624 of the moving part 62. The movable fingers 622 and the fixed fingers 642 can be made of conductive materials or include conductive elements. Therefore, the movable fingers 622 and the fixed fingers 642 are conductive, and a capacitor is formed between the moving part 62 and the fixed part 64. The capacitor between the moving part 62 and the fixed part 64 is formed based on the overlap of the movable fingers 622 and the fixed fingers 642. At a position perpendicular to Figure 2 In the plane shown, for zero AC sound pressure applied to the diaphragm 30, there is a fixed limited overlap between the movable finger 622 and the fixed finger 642. When AC sound pressure is applied to the diaphragm 30, the movable finger 622 moves along a direction perpendicular to the Figure 2 The movable finger 622 moves in the direction of the plane shown in the figure, changing the overlap amount with the fixed finger 642. Figure 2 The farther the direction of the plane is from the fixed finger 642, the smaller the overlap with the second gap 644, and the smaller the capacitance. Figure 2 In the direction perpendicular to the plane shown, the closer the movable finger 622 is to the fixed finger 642, the greater the capacitance is, and in response to the change in capacitance, an electrical signal will be generated and output.

[0036] See also Figure 3 A schematic diagram of a cantilever of a MEMS according to a second embodiment of the present invention, wherein a plurality of cantilevers 40 are arranged in a linear array, and each cantilever 40 has a rectangular shape. For a linear array of rectangular cantilevers 40 , each pair of cantilevers 40 can be attached to a single diaphragm 30 .

[0037] Figure 4 and Figure 5 The deformation of the diaphragm 30 and the cantilever 40 is shown when the diaphragm 30 receives an AC sound wave entering the microphone. Figure 4 The deformation of the diaphragm 30 and the cantilever 40 when negative pressure is applied to the diaphragm 30 is shown. Figure 5 FIG. 4 shows the deformation of the diaphragm 30 and the cantilever 40 when a positive pressure is applied. Figure 4 and Figure 5As shown, when the diaphragm 30 moves under the pressure difference between the inner surface and the outer surface of the diaphragm 30, the first end 42 of the cantilever 40 is pulled upward or pushed downward by the plunger 50, so that the cantilever 40 pivots around the fulcrum 46, and the second end 44 of the cantilever 40 moves downward or upward together with the moving part 62 of the sensor element 60, thereby changing the overlap between the movable finger 622 and the fixed finger 642. Since the distance between the second end 44 and the fulcrum 46 is much greater than the distance between the first end 42 and the fulcrum 46, the displacement of the diaphragm 30 is effectively amplified, and the sensitivity of the micro-electromechanical system 10 is improved.

[0038] Figure 6 and Figure 7 The working principle of the hinge cantilever 40 is shown. Each hinge cantilever 40 is made of a thin silicon wafer, and a bending portion 47 and a fulcrum 46 are provided at the slit of the thin silicon wafer. The fulcrum 46 extends to the sensing area next to the rib 48. Since the cavity 22 is in a low pressure or vacuum state, there is limited or no sound in the cavity 22, so these ribs 48 are designed to be strong, light and low inertia. When the diaphragm 30 moves z1, the second end 44 of the cantilever 40 together with the moving part 62 of the sensor element 60 moves z2 in the opposite direction, where z2 is greater than z1, thereby improving the mechanical sensitivity of the micro-electromechanical system 10 using the cantilever 40.

[0039] In the above embodiment, the size of the opening 24 is smaller than the size of the cavity 22. Therefore, under standard atmospheric pressure (1atm), the small diameter and thick diaphragm 30 avoids mechanical collapse and very large DC deformation, and its stiffness is one order of magnitude higher than that of a conventional diaphragm. The micro-electromechanical system 10 uses a cantilever 40 to amplify the displacement of the diaphragm 30 by at least about 10 times or more, which is very suitable for the circumference of a comb-tooth drive, and can achieve improved electrostatic sensitivity. The hinged cantilevers 40 can be arranged in a circular array, in which case each cantilever 40 is triangular or fan-shaped; or each cantilever 40 is a linear array, in which case each cantilever 40 is rectangular. The first end 42 of each cantilever 40 is connected to the diaphragm 30, and the second end 44 is connected to the moving part 62 of the sensing element 60. Generally speaking, the diaphragm 30 array is all connected to the center of the plunger 50 that drives the hinge cantilever 40 array. The cantilever 40 can be connected to various electrostatic sensing components, but because the moving part 62 of the comb-drive sensor element 60 has high sensitivity and a large allowable range of motion in the z direction, a comb drive with spaced fingers is preferred.

[0040] In order to further improve the mechanical sensitivity of the MEMS 10, a hinged cantilever 40 can be used, with one hinged cantilever 40 driving the next stage, thereby producing a greater amplification effect. This hinged cantilever 40 can be optimized to achieve nonlinear displacement amplification of the diaphragm 30, so that the initial large DC displacement caused by atmospheric pressure is not amplified as when the DC pressure is between 0.5-1 times the standard atmospheric pressure. This will be a passive DC type of control.

[0041] like Figure 8-9 , a cross-sectional view of a micro-electromechanical system according to a third embodiment of the present invention. The micro-electromechanical system 10 includes a series of multi-stage cantilevers 40 connected in series. In this embodiment, the multi-stage cantilever 40 includes a first-stage cantilever 40a, a second-stage cantilever 40b, and a third-stage cantilever 40c. The first end 42a of the first-stage cantilever 40a is connected to the first plunger 50a. The second end 44a of the first-stage cantilever 40a is connected to the first end 42b of the second-stage cantilever 40b through the second plunger 50b, and the second end 44b of the second-stage cantilever 40b is connected to the first end 42c of the third-stage cantilever 40c through the third plunger 50c. The second end 44c of the third-stage cantilever 40c is connected to the moving part 62 of the sensing element 60. The fulcrums 46a, 46b, and 46c are respectively arranged between the first end 42 and the second end 44 of the cantilever 40. The distances between the first ends 42a, 42b, 42c and the pivot points 46a, 46b, 46c are respectively smaller than the distances between the second ends 44a, 44b, 44c and the pivot point 46. Assuming that the distance between the second end 44a and the pivot point 46a is n1 times the distance between the first end 42a and the pivot point 46a, the distance between the second end 44b and the pivot point 46b is n2 times the distance between the first end 42b and the pivot point 46b, and the distance between the second end 44c and the pivot point 46c is n3 times the distance between the first end 42c and the pivot point 46c, when the diaphragm 30 moves under the pressure difference between the inner surface and the outer surface of the diaphragm 30, the moving part 62 of the sensing element 60 will achieve a displacement, which is substantially n1*n2*n3 times the displacement of the diaphragm 30. The displacement of the diaphragm 30 is greatly amplified.

[0042] The MEMS 10 disclosed above has the advantages of high signal-to-noise ratio, small package volume, and normal or high sensitivity. By increasing the mechanical sensitivity, it is easier to achieve the standard (-38 dB V / Pa) or higher total sensor sensitivity required for the vacuum back cavity volume design. By making the cavity / back cavity volume a vacuum, it does not need to be larger than the conventional front volume and can be much smaller than the conventional front volume. This increases the possibility of using a microphone with a higher signal-to-noise ratio in a smaller package size than conventionally used, which is very attractive for all microphone applications, especially mobile applications.

[0043] The above is a detailed introduction to the micro-electromechanical system disclosed in the embodiment of the present invention. Specific examples are used in this article to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only used to help understand the micro-electromechanical system of the present invention and its core concept. At the same time, for those skilled in the art, according to the concept of the present invention, there will be changes in the specific implementation methods and application scopes. In summary, the content of this specification should not be understood as limiting the present invention.

Claims

1. A micro-electromechanical system, It is characterized in that include: a housing defining a cavity and an opening communicating with the cavity; a diaphragm mounted at the opening; at least one cantilever disposed in the cavity, the cantilever comprising a first end, a second end, and a fulcrum disposed between the first end and the second end; a plunger, the plunger being located between the diaphragm and the cantilever for transmitting the displacement of the diaphragm to the first end of the cantilever; and The sensing element comprises a fixed part fixed relative to the housing and a movable part connected to the second end of the cantilever and movable relative to the fixed part, wherein the movable part comprises a plurality of conductive movable fingers, and a first gap is formed between every two adjacent movable fingers; the fixed part comprises a plurality of conductive fixed fingers, and a second gap is formed between every two adjacent fixed fingers; the plurality of movable fingers are respectively aligned with the plurality of second gaps of the fixed part, and the plurality of fixed fingers are respectively aligned with the plurality of first gaps of the movable part; Wherein, the distance between the first end and the fulcrum is smaller than the distance between the second end and the fulcrum.

2. The micro-electromechanical system according to claim 1, It is characterized in that The cavity is hermetically sealed, and the internal pressure of the cavity is less than the external atmospheric pressure.

3. The micro-electromechanical system according to claim 2, It is characterized in that The cavity is evacuated.

4. The micro-electromechanical system according to claim 1, It is characterized in that The cantilever comprises a plurality of triangular or fan-shaped cantilever arms arranged in a circular array.

5. The micro-electromechanical system according to claim 1, It is characterized in that The cantilever includes a pair of rectangular cantilevers arranged in a linear array.

6. The micro-electromechanical system according to claim 1, It is characterized in that The cantilever further includes at least one rib disposed at a surface thereof.

7. The micro-electromechanical system according to claim 1, It is characterized in that The micro-electromechanical system further includes a support member disposed between the fulcrum and the housing.

8. The micro-electromechanical system according to claim 1, It is characterized in that The size of the opening is smaller than the size of the cavity.

9. The micro-electromechanical system according to claim 1, It is characterized in that The cantilever comprises a plurality of cantilevers connected in series.

10. The micro-electromechanical system according to claim 9, It is characterized in that The multi-stage cantilever includes a first-stage cantilever, a second-stage cantilever and a third-stage cantilever, wherein the first end of the first-stage cantilever is connected to the first plunger, the second end of the first-stage cantilever is connected to the first end of the second-stage cantilever through the second plunger, the second end of the second-stage cantilever is connected to the first end of the third-stage cantilever through the third plunger, and the sensing element is connected to the second end of the third-stage cantilever.

11. The micro-electromechanical system according to claim 10, It is characterized in that The first-stage cantilever, the second-stage cantilever and the third-stage cantilever each include a fulcrum located between the first end and the second end thereof, and a support member arranged between the fulcrum and the housing.

12. The micro-electromechanical system according to claim 1, It is characterized in that The first end includes a curved portion having a low thickness.

13. The micro-electromechanical system according to claim 1, Features: The first end includes a bend having one or more slots.

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