CN111757227A

CN111757227A - MEMS microphone

Info

Publication number: CN111757227A
Application number: CN202010641465.0A
Authority: CN
Inventors: 赵转转; 柏杨; 但强; 王凯杰; 李杨; 张睿
Original assignee: Ruisheng Technology Nanjing Co Ltd
Current assignee: AAC Technologies Holdings Nanjing Co Ltd; Ruisheng Technology Nanjing Co Ltd
Priority date: 2020-07-06
Filing date: 2020-07-06
Publication date: 2020-10-09
Also published as: WO2022006999A1

Abstract

The invention provides an MEMS microphone, which comprises a base with a back cavity, a vibrating diaphragm arranged at an interval with the base, and a back plate covering the vibrating diaphragm and having an inner cavity with the vibrating diaphragm at an interval; the back plate comprises a fixing part and a main body part which is surrounded by the fixing part and connected with the fixing part, and the central area of the main body part is bulged towards the direction far away from the vibrating diaphragm to form a bulge part. The existence of bellying has increased the distance of main part with the vibrating diaphragm, and after the sound wave air current got into the inner chamber through the acoustics hole, the sound wave air current velocity of flow was less than the average airflow velocity of inner chamber in the inner chamber that the arch corresponds to reduced the press mold damping, and then reduced MEMS microphone's mechanical noise.

Description

MEMS microphone

[ technical field ] A method for producing a semiconductor device

The invention relates to the technical field of acoustics, in particular to an MEMS (micro-electromechanical system) microphone.

[ background of the invention ]

In a MEMS (Micro Electro mechanical System) microphone in the prior art, a vibrating diaphragm is disposed on a base at intervals, and a back plate is disposed above the vibrating diaphragm at intervals in an inner cavity. The vibrating diaphragm and the back plate are parallel to each other, and a flat capacitor system is formed. When sound wave airflow enters an inner cavity between the back plate and the vibrating diaphragm, sound pressure acts on the vibrating diaphragm to cause the vibrating diaphragm to move, the distance between the film and the back plate is changed through the movement, then the capacitor is changed, the capacitor is finally converted into an electric signal, and finally the corresponding function of the microphone is achieved. However, because the cavity between the diaphragm and the backplate is small, the air flow near the edges of the diaphragm and backplate when air flows is less than the air flow in the central region of the cavity, i.e., squeeze film damping exists when air flows between the diaphragm and the backplate. The squeeze film damping has a great influence on the dynamic response of the MEMS chip, and the larger the damping is, the larger the mechanical noise is.

Therefore, it is necessary to provide a MEMS microphone to solve the problem of large damping of the piezoelectric film in the MEMS chip.

[ summary of the invention ]

The invention aims to provide a MEMS microphone.

The technical scheme of the invention is as follows: the MEMS microphone comprises a base with a back cavity, a vibrating diaphragm arranged at an interval with the base, and a back plate covering the vibrating diaphragm and having an inner cavity with the vibrating diaphragm at an interval; the back plate comprises a fixing part and a main body part which is surrounded by the fixing part and connected with the fixing part, and the central area of the main body part is bulged towards the direction far away from the vibrating diaphragm to form a bulge part.

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

More preferably, the convex portion is in the shape of a circular arc surface.

Preferably, the main body portion has a plurality of spaced acoustic holes formed therethrough.

Preferably, a first insulating layer is arranged between the diaphragm and the back plate, and the fixing portion is fixedly connected with the first insulating layer.

Preferably, a second insulating layer and a plurality of etching barrier walls are arranged between the diaphragm and the base.

The invention has the beneficial effects that: the central area of the backboard main body part bulges to form a bulge part in the direction far away from the vibrating diaphragm, so that the distance between the position of the backboard with the bulge part and the vibrating diaphragm is larger than the average distance between the backboard and the vibrating diaphragm. The design enables the air flow velocity in the inner cavity corresponding to the protruding part to be smaller than the average air flow of the inner cavity, so that the squeeze film damping in the inner cavity is reduced, and the mechanical noise of the MEMS chip is reduced.

[ description of the drawings ]

Fig. 1 is a cross-sectional view of a MEMS microphone according to an embodiment of the present invention.

[ detailed description ] embodiments

The invention is further described with reference to the following figures and embodiments.

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

The back plate 4 comprises a fixing portion 46 and a main body portion 45 surrounded by and connected to the fixing portion 46, the fixing portion 46 of the back plate being an edge of the back plate 4, wherein the main body portion 45 is disposed at intervals. A first insulating layer 6 is arranged between the back plate 4 and the diaphragm 2, so that the back plate 4 is isolated from the diaphragm 2, and the fixing portion 46 is fixedly connected with the first insulating layer 6.

A second insulating layer 21 is arranged between the diaphragm 2 and the base 1, thereby isolating 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 with the base 1 through the second insulating layer 21, only the edge end of the diaphragm 2 is connected with the second insulating layer 21, and the position where the diaphragm 2 is not fixedly connected with the second insulating layer 21 can vibrate freely, that is, the central area of the diaphragm 2 can vibrate freely, so that 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, the diaphragm 2 and the base 1 are spaced apart to form a gap. The displacement space in which the diaphragm 2 vibrates is increased.

An inner cavity 3 is formed between the back plate 4 (i.e., the body portion 45) and the diaphragm 2, and a capacitor is present in the inner cavity 3. When the vibrating diaphragm 2 vibrates, the height of the inner cavity 3 in the direction perpendicular to the vibrating diaphragm 2 is changed, the capacitance value of the inner cavity 3 is further changed, the change of the capacitance is converted into a digital signal, and finally the function of the microphone is achieved.

In a modified embodiment, a plurality of etching barrier walls 5 may be further disposed between the diaphragm 2 and the base 1, and the etching barrier walls 5 may ensure a reliable stop of an etching process that may occur in a manufacturing process, thereby protecting the second insulating layer 21 from being etched away. The etching barrier walls 5 are arranged at intervals, and a second insulating layer 21 is arranged between every two etching barrier walls 5. The second insulating layer 21 and the etching barrier wall 5 support the diaphragm 2 together, so that the diaphragm 2 and the base 1 form a gap at intervals. The etch barrier 5 may typically be made of, for example, oxide, thermal oxide, or TEOS. Its thickness may be between 0.1 and 1 μm.

Further, the backplate 4 has at least one convex portion 41 bulging in a direction away from the diaphragm 2. In one embodiment, the central region of the main body 45 is formed with a protrusion 41 protruding away from the diaphragm 2; there is electric capacity in the inner chamber 3 between backplate 4 and vibrating diaphragm 2, when vibrating diaphragm 2 takes place to vibrate, the distance between vibrating diaphragm 2 and backplate 4 changes for electric capacity in inner chamber 3 changes, and the electric potential on the vibrating diaphragm 2 that constitutes inner chamber 3 electric capacity will change, and the electric potential of change converts the signal of telecommunication into.

Specifically, the central axis of the protrusion 41 coincides with the central axis of the main body 45, and the distance from the main body 45 to the diaphragm 2 decreases gradually from the central position of the main body 45 toward the fixing portion 46. The back plate 4 is raised from the connection position with the first insulating layer 6 in a direction away from the diaphragm 2 to form a raised portion 41 having a circular arc shape, and the raised portion 41 is raised up to a vertex of a central region of the main body portion 45. Since the central axis of the protrusion 41 coincides with the central axis of the main body 45, the distance between the center of the protrusion 41 and the diaphragm 2 is the farthest, that is, the cavity 3 has the largest height on the central axis. After the sound wave airflow enters the inner cavity 3 through the acoustic hole 42, the central area of the main body part 45 is bulged upwards, so that the central volume of the inner cavity 3 is increased, the flow speed of the sound wave airflow at the center of the inner cavity 3 is not larger than the average flow speed in the inner cavity 3, the squeeze film damping in the inner cavity 3 is reduced to be negligible, and the mechanical noise of the MEMS microphone is reduced.

Preferably, the main body 45 of the backplate 4 is uniformly provided with acoustic holes 42 penetrating through the backplate 4, the acoustic holes 42 communicate the inner cavity 3 with the atmosphere of the external environment, the acoustic holes 42 are small through holes, so that the sound wave airflow can enter or flow out of the inner cavity 3, the acoustic holes 42 are uniformly distributed on the backplate 4, and when the sound wave airflow is transmitted, the sound wave airflow passes through the acoustic holes 42 and enters the inner cavity 3.

Preferably, the cross section of the back cavity 11 is an inverted isosceles trapezoid. The back cavity 11 has atmospheric pressure, and when the diaphragm 2 vibrates, the pressure in the back cavity 11 is constant, so that the free vibration of the diaphragm 2 is maintained.

The diaphragm 2 is arranged on the base 1 with the back cavity 11 at intervals of the second insulating layer 21, so that a gap exists between the diaphragm 2 and the base 1, and the diaphragm 2 is ensured to have enough vibration space. A back plate 4 having an acoustic hole 42 is provided above the diaphragm 2 with the cavity 3 interposed therebetween, and a boss 41 is formed on the back plate 4. Because the inner chamber 3 is arranged between the diaphragm 2 and the backboard 4, the height of the inner chamber 3 along the direction perpendicular to the diaphragm 2 on the central axis is increased by the bulge part 41, when the sound wave airflow enters the inner chamber 3 through the acoustic hole 42, the sound wave airflow flows in the inner chamber 3, the central area of the inner chamber 3 is increased to the average height greater than the inner chamber 3 due to the height, thereby the airflow velocity of the central area of the inner chamber 3 is reduced, and further the squeeze film damping in the squeeze film damping inner chamber 3 of the central area of the inner chamber 3 is reduced, and the mechanical noise of the MEMS microphone is also reduced.

While the foregoing is directed to embodiments of the present invention, it will be understood by those skilled in the art that various changes may be made without departing from the spirit and scope of the invention.

Claims

1. An MEMS microphone comprises a base with a back cavity, a vibrating diaphragm arranged at an interval with the base, and a back plate covering the vibrating diaphragm and having an inner cavity with the vibrating diaphragm at an interval; the back plate is characterized by comprising a fixing part and a main body part which is surrounded by the fixing part and connected with the fixing part, and the central area of the main body part bulges in the direction far away from the vibrating diaphragm to form a bulge part.

2. The MEMS microphone of claim 1, wherein a distance from the main body portion to the diaphragm decreases gradually from a center position of the main body portion toward the fixing portion.

3. The MEMS microphone of claim 2, wherein the protrusion is in the shape of a circular arc.

4. The MEMS microphone of claim 2, wherein the body portion has a plurality of spaced acoustic holes formed therethrough.

5. The MEMS microphone of claim 1, wherein a first insulating layer is disposed between the diaphragm and the backplate, and the fixing portion is fixedly connected to the first insulating layer.

6. The MEMS microphone of claim 1, wherein a second insulating layer and a plurality of etching barrier walls are disposed between the diaphragm and the base.