WO2022007000A1

WO2022007000A1 - Mems microphone

Info

Publication number: WO2022007000A1
Application number: PCT/CN2020/103746
Authority: WO
Inventors: 赵转转; 柏杨; 但强; 王凯杰; 李杨; 张睿
Original assignee: 瑞声声学科技(深圳)有限公司; 瑞声科技（南京）有限公司
Priority date: 2020-07-06
Filing date: 2020-07-23
Publication date: 2022-01-13
Also published as: CN111757228A

Abstract

Provided is a MEMS microphone. The MEMS microphone comprises a base having a back cavity, a diaphragm arranged separate from the base with a gap therebetween, and a back panel covering the diaphragm and arranged separate from the diaphragm with an inner cavity therebetween. The back panel comprises at least one protruding portion protruding in the direction away from the diaphragm. The presence of the protruding portion increases the distance between the back panel and the diaphragm, such that after an acoustic wave airflow passes through an acoustic hole and enters the inner cavity, the flow rate of the acoustic wave airflow in the inner cavity corresponding to the protruding portion is smaller than the average airflow rate in the inner cavity, thereby lowering the pressure film damping and reducing the mechanical noise of the MEMS microphone.

Description

A MEMS microphone

technical field

The invention relates to the technical field of acoustics, in particular to a MEMS microphone.

Background technique

A MEMS (Micro Electro Mechanic System, Micro Electro Mechanical System) microphone in the prior art is provided with a vibrating membrane at intervals on the base, and a back plate is provided above the vibrating membrane and further apart from the inner cavity. The diaphragm and the back plate are parallel to each other, forming a flat capacitive system. When the sound wave airflow enters the cavity between the back plate and the diaphragm, the sound pressure acts on the diaphragm and causes the diaphragm to move. This movement changes the distance between the film and the back plate, thereby changing the capacitance and finally converting it into an electrical signal. Finally, the corresponding function of the microphone is realized.

technical problem

However, due to the small cavity between the diaphragm and the back plate, the air velocity near the edge of the diaphragm and the back plate is smaller than the air velocity in the central area of the inner cavity when the air flows, that is, the air flows between the diaphragm and the back plate. Laminate damping. The compression film damping has a great influence on the dynamic response of the MEMS chip. The greater the damping, the greater the mechanical noise.

Therefore, it is necessary to provide a MEMS microphone to solve the situation that the damping of the pressure film in the MEMS chip is relatively large.

technical solutions

An object of the present invention is to provide a MEMS microphone that reduces mechanical noise.

The technical solution of the present invention is as follows: a MEMS microphone, the MEMS microphone includes a base with a back cavity, a vibrating membrane arranged at intervals from the base, and a vibrating membrane covering the vibrating membrane and being spaced from the vibrating membrane A back plate with an inner cavity; the back plate has at least one convex portion raised in a direction away from the diaphragm.

More preferably, the at least one protruding portion includes a first protruding portion, and the back plate includes a fixing portion and a main body portion surrounded by and connected to the fixing portion, the fixing portion facing away from the diaphragm. The first raised portion is formed by bulging in the direction of .

More preferably, the first protruding portion is located on the outer periphery of the fixing portion.

More preferably, the first protruding portion is spaced apart from the outer periphery of the fixing portion.

More preferably, the at least one protruding portion further includes a second protruding portion, and the main body portion of the back plate is raised in a direction away from the diaphragm to form the second protruding portion.

More preferably, the distance from the main body portion to the diaphragm gradually decreases from the central position of the main body portion to the direction of the fixing portion.

More preferably, the main body of the back plate is provided with an acoustic hole that communicates the inner cavity and the external environment.

More preferably, a first insulating layer is provided between the diaphragm and the back plate, and the fixing portion is fixedly connected to the first insulating layer.

More preferably, a second insulating layer and several etching barrier walls are arranged between the diaphragm and the base.

beneficial effect

The beneficial effect of the present invention is that: the back plate has at least one raised portion protruding in the direction away from the vibrating film, so that the distance between the position where the back plate has the raised portion and the vibrating film is greater than the distance between the back plate and the vibrating film average distance between. This design makes the air velocity of the inner cavity corresponding to the raised portion smaller than the average velocity of the airflow in the inner cavity, thereby reducing the pressure film damping in the inner cavity and reducing the mechanical noise of the MEMS chip.

Description of drawings

FIG. 1 is a cross-sectional view of a MEMS microphone according to Embodiment 1 of the present invention.

FIG. 2 is a cross-sectional view of a MEMS microphone according to Embodiment 2 of the present invention.

FIG. 3 is a cross-sectional view of a MEMS microphone according to Embodiment 3 of the present invention.

FIG. 4 is a cross-sectional view of a MEMS microphone according to Embodiment 4 of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be further described below with reference to the accompanying drawings and embodiments.

Referring to FIG. 1 , in the first embodiment of the present invention, the MEMS microphone includes a base 1 having a back cavity 11 , a diaphragm 2 and a back plate 4 sequentially arranged on the surface of the base 1 .

The backplane 4 includes a fixed portion 46 and a main body portion 45 surrounded by and connected to the fixed portion 46 . The fixed portion 46 of the backplane is the edge of the backplane 4 , wherein the main body portions 45 are arranged at intervals. A first insulating layer 6 is provided between the back plate 4 and the vibrating membrane 2 , so as to isolate the back plate 4 from the vibrating membrane 2 , and the fixing portion 46 is fixedly connected to the first insulating layer 6 .

A second insulating layer 21 is disposed between the diaphragm 2 and the base 1 to isolate the diaphragm 2 from the base 1 , and the first insulating layer 6 at least partially covers the second insulating layer 21 . The edge of the diaphragm 2 is connected to the base 1 through the second insulating layer 21 , only the edge end of the diaphragm 2 is connected to the second insulating layer 21 , and the position where the diaphragm 2 is not fixedly connected to the second insulating layer 21 can be Free vibration is performed, that is to say, the central area of the diaphragm 2 can vibrate freely, and the vibration effect of the diaphragm 2 is maintained. Since the second insulating layer 21 is disposed between the diaphragm 2 and the base 1 , a gap is formed between the diaphragm 2 and the base 1 . The displacement space for the vibration of the diaphragm 2 is increased.

An inner cavity 3 is formed between the back plate 4 (ie, the main body portion 45 ) and the diaphragm 2 , and a capacitor exists in the inner cavity 3 . When the diaphragm 2 vibrates, the height of the inner cavity 3 in the direction perpendicular to the diaphragm 2 is changed, thereby changing the capacitance value of the inner cavity 3, and the change of the capacitance is converted into a digital signal, and finally the function of the microphone is realized.

In a modified embodiment, a plurality of etching barrier walls 5 may also be arranged between the diaphragm 2 and the base 1, and the etching barrier walls 5 can ensure a reliable stop of the etching process that may occur in the manufacturing process, thereby protecting the second The insulating layer 21 is not etched away. A plurality of etching stop walls 5 are arranged at intervals, and a second insulating layer 21 is provided between every two etching stop walls 5 . The second insulating layer 21 and the etching barrier wall 5 jointly support the diaphragm 2 , so that the diaphragm 2 and the base 1 are spaced to form a gap. The etch stop wall 5 can typically be made of, for example, oxide, thermal oxide, or TEOS. Its thickness can be between 0.1 and 1 μm.

At the position where the main body portion 45 is close to the fixing portion 46 and is spaced apart from the outer periphery of the fixing portion 46 , there is provided a first protruding portion 41 that protrudes in a direction away from the diaphragm 2 , and the first protruding portion 41 is in the inner cavity 3 . The corresponding position has a higher height, thereby increasing the distance between the back plate 4 and the diaphragm 2 at the first raised portion 41 . When the sound wave airflow enters the inner cavity 3 through the acoustic hole 42 , the airflow can enter under the raised first protrusion 41 at the edge of the inner cavity 3 , so that the air in the inner cavity 3 is not compressed, thereby reducing the amount of air in the inner cavity 3 . The compression film damping reduces the mechanical noise of MEMS microphones.

More preferably, acoustic holes 42 penetrating the back plate 4 are evenly spaced on the back plate 4, the acoustic holes 42 communicate with the inner cavity 3 and the external environment, and the acoustic holes 42 are small through holes, so that the sound wave airflow can enter or Flowing out of the inner cavity 3 , the acoustic holes 42 are evenly distributed on the back plate 4 . When the sound wave air flow is transmitted to the MEMS microphone, the sound wave air flow passes through the acoustic hole 42 and enters the inner cavity 3 . On the whole, the entire back plate 4 is like a net with densely arranged holes in the middle.

Referring to FIG. 1 , the cross section of the back cavity 11 is an inverted isosceles trapezoid. The back cavity 11 has atmospheric pressure. When the vibrating membrane 2 vibrates, the pressure in the back cavity 11 does not change, so that the free vibration of the vibrating membrane 2 is maintained.

Please continue to refer to FIG. 1 , the cross section of the first raised portion 41 is a similar isosceles triangle, and the structure of a similar sun hat or an isosceles triangle can be used to enhance the structural strength of the first raised portion 41 , so that the first raised portion 41 has a similar structure. The portion 41 is not easily deformed.

As shown in FIG. 2 , in the second embodiment of the present invention, the first protruding portion 41 ′ is disposed at the position of the outer peripheral edge of the fixing portion 46 of the back plate 4 , and protrudes from the fixing portion 46 of the back plate in a direction away from the diaphragm 2 . Compared with the first embodiment, the position of the first raised portion 41 ′ has changed, but the functions of the first raised portion 41 of the first embodiment and the first raised portion 41 ′ of the second embodiment are both used to The edge position of the inner cavity 3 is perpendicular to the direction of the diaphragm 2 and the height space increases. After the sound wave airflow enters the inner cavity 3 through the acoustic hole 42, the sound wave airflow flows in the inner cavity 3. Due to the arrangement of the first protrusions (41, 41'), the edge of the inner cavity 3 is perpendicular to the diaphragm 2. The height space of the direction is increased, and the sound wave airflow no longer forms air compression at the edge of the inner cavity 3, thereby reducing the pressure film damping at the edge of the inner cavity 3. After the compression film damping in the inner cavity 3 is reduced, the mechanical noise of the MEMS microphone is also reduced.

More preferably, referring to FIG. 3 , based on the first implementation, a second convex portion 43 is further provided in the central area of the main body portion 45 . The second convex portion 43 is raised in the direction away from the diaphragm 2 . The central axis of the raised portion 43 coincides with the central axis of the main body portion 45 and the diaphragm 2 . The second raised portion 43 protrudes and extends from the bottom of the first raised portion 41 toward the central axis of the main body portion 45 , and gradually rises to form the second raised portion 43 , until the center of the main body portion 45 becomes the second raised portion 43 The apex of the bulge. More specifically, the second protrusion 43 is formed by the bulge in the middle of the main body portion 45 , and the distance from the main body portion 45 to the diaphragm 2 gradually decreases from the center position of the main body portion 45 to the direction of the fixing portion 46 . The second raised portion 43 makes the height of the central region of the inner cavity 3 in the direction perpendicular to the diaphragm 2 greater than the average height of the inner cavity 3 . When the acoustic air flow enters the inner cavity 3 through the acoustic hole 42 , the flow velocity of the air flow in the central area of the inner cavity 3 is not greater than the average flow velocity in the inner cavity 3 , thereby reducing the pressure film damping in the inner cavity 3 .

Specifically, referring to FIG. 3 , the second protruding portion 43 is in the shape of an arc surface, and is formed by bulging from the central area of the body portion 45 to the direction away from the diaphragm 2 ; the back plate fixing portion 46 is fixedly connected to the first insulating On layer 6, since the cross section of the second raised portion 43 is in the shape of an arch bridge, the central part of the main body portion 45 is supported by the arch bridge shape and will not collapse downward, so that the central region of the main body portion 45 and the diaphragm 2 are kept relatively close. great distance. The height of the central area of the inner cavity 3 is greater than the average height of the inner cavity 3. When the acoustic wave flows in the inner cavity 3, the airflow velocity in the central area of the inner cavity 3 is the smallest, thereby reducing the pressure film damping in the central area of the inner cavity 3. .

Referring to FIG. 4 , based on the second embodiment, a second protruding portion 43 is also provided in the central region of the main body portion 45 . The second raised portion 43 is disposed in the central area of the main body portion 45 . The second raised portion 43 extends from the central area to the edge of the back plate 4 and gradually reduces the height of the raised portion. The edge of the second raised portion 43 is connected to the first raised portion. The hypotenuse of the raised portion 41' is connected. Protrusions are provided on both the central area of the back plate 4 and the fixing portion 46 , which can improve the space size of the inner cavity 3 , thereby reducing the compression film damping in the inner cavity 3 .

The above are only the embodiments of the present invention. It should be pointed out that for those of ordinary skill in the art, improvements can be made without departing from the inventive concept of the present invention, but these belong to the present invention. scope of protection.

Claims

A MEMS microphone, the MEMS microphone comprising a base with a back cavity, a vibrating membrane spaced from the base, and a back plate covering the vibrating membrane and having an inner cavity spaced from the vibrating membrane; It is characterized in that, the back plate has at least one raised portion protruding in a direction away from the diaphragm.
The MEMS microphone of claim 1, wherein the at least one protruding portion comprises a first protruding portion, the back plate comprises a fixing portion and a main body portion surrounded by and connected to the fixing portion, The fixing portion protrudes in a direction away from the diaphragm to form the first protruding portion.
The MEMS microphone of claim 2, wherein the first protruding portion is located on an outer periphery of the fixing portion.
The MEMS microphone according to claim 2, wherein the first protruding portion is spaced apart from the outer periphery of the fixing portion.
The MEMS microphone according to claim 2, wherein the at least one protruding portion further comprises a second protruding portion, and the main body portion of the back plate is raised in a direction away from the diaphragm to form the the second protrusion.
The MEMS microphone according to claim 5, wherein the distance from the main body portion to the diaphragm gradually decreases from the central position of the main body portion to the direction of the fixing portion.
The MEMS microphone according to claim 6, wherein the main body of the back plate is provided with an acoustic hole that communicates with the inner cavity and the external environment.
The MEMS microphone according to claim 1, wherein a first insulating layer is provided between the diaphragm and the back plate, and the fixing portion is fixedly connected to the first insulating layer.
The MEMS microphone according to claim 1, wherein a second insulating layer and a plurality of etching barrier walls are arranged between the diaphragm and the base.