US20170280263A1

US20170280263A1 - In-plane overtravel stops for mems microphone

Info

Publication number: US20170280263A1
Application number: US15/620,166
Authority: US
Inventors: Zhijun Guo; Andrew J. Doller
Original assignee: Robert Bosch GmbH; Akustica Inc
Current assignee: Robert Bosch GmbH; Akustica Inc
Priority date: 2015-06-17
Filing date: 2017-06-12
Publication date: 2017-09-28
Also published as: US9681243B2; US20160373874A1; WO2016202661A1

Abstract

MEMS microphones and MEMS devices. In one embodiment, the MEMS microphone includes a membrane and a layer. The membrane is coupled to a support. The layer includes a backplate and an overtravel stop. The backplate is coupled to the support. The overtravel stop is coupled to the membrane and is physically separated from the backplate by a gap in a radial direction. The overtravel stop has a first end that is oriented proximal to the membrane and a second end that is oriented distal to the membrane. The second end flares outward to restrict movement of the membrane in the radial direction by contacting the backplate.

Description

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No. 14/742,308, entitled “IN-PLANE OVERTRAVEL STOPS FOR MEMS MICROPHONE” filed Jun. 17, 2015, which is incorporated herein by reference in its entirety.

BACKGROUND

Embodiments of the disclosure relate to microelectricalmechanical (MEMS) microphones and methods of their construction. In particular, embodiments of the disclosure relate to constructions of overtravel stops for a MEMS microphone membrane.
Capacitive MEMS microphones are mechanically sensitive devices. They operate over a wide input dynamic range, for example, 60-130 dB SPL. A membrane that is sensitive enough to detect the lowest pressures (e.g., 1 mPa) must withstand larger pressure fluctuations. Large pressure fluctuations may occur due to, for example, impacts, vibration, vacuum, over pressure, and acoustic pulses due to air discharge near the port hole. The membrane must withstand pressures in the range of several 10 s of Pascals without being destroyed. This is typically achieved by adapting the membrane to contact overtravel stops (OTS) to prevent excessive movement in a direction of applied acoustic pressure. However, these designs may not provide overtravel protection for the membrane in other directions.

SUMMARY

Embodiments of the disclosure provide for various constructions of overtravel stops that are configured to restrict movement of the membrane of the microelectricalmechanical (MEMS) microphone in multiple directions. In particular, the overtravel stops restrict movement of the membrane in a radial direction with respect to the membrane. The overtravel stops are located on a backplate layer of the MEMS microphone. During manufacturing of the MEMS microphone, the overtravel stops are separated from the backplate layer with a precise gap between the backplate layer and the overtravel stop. The gap allows for a predetermined range of movement of the overtravel stop before it contacts a backplate. In addition, the overtravel stop is mechanically connected to the membrane of the MEMS microphone. Therefore, movement of the membrane is also restricted by the range of movement of the overtravel stop. In this way, the overtravel stop provides a structure that protects the membrane from damage caused by overtravel.
One embodiment provides a MEMS microphone. In one embodiment, the MEMS microphone includes a membrane and a layer. The membrane is coupled to a support. The layer includes a backplate and an overtravel stop. The backplate is coupled to the support. The overtravel stop is coupled to the membrane and is physically separated from the backplate by a gap in a radial direction. The overtravel stop has a first end that is oriented proximal to the membrane and a second end that is oriented distal to the membrane. The second end flares outward to restrict movement of the membrane in the radial direction by contacting the backplate.
Another embodiment provides a MEMS device. In one embodiment, the MEMS device includes a movable structure and a layer. The movable structure is coupled to a support. The layer includes a rigid structure and an overtravel stop. The rigid structure is coupled to the support. The overtravel stop is coupled to the movable structure and is physically separated from the movable structure by a gap in a radial direction. The rigid structure has a first end that is oriented proximal to the movable structure and a second end that is oriented distal to the movable structure. The second end flares outward to restrict movement of the movable structure in the radial direction by contacting the rigid structure.
Other aspects of the disclosure will become apparent by consideration of the detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an embodiment of a MEMS microphone including a plurality of overtravel stops positioned around a perimeter of a membrane of the MEMS microphone.

FIG. 2 is an illustration of the membrane of the MEMS microphone of FIG. 1.

FIG. 3 is an illustration of a spring of the MEMS microphone of FIG. 1.

FIG. 4 is an illustration of a backplate layer including a backplate and the plurality of overtravel stops of FIG. 1.

FIG. 5 is a detailed view of one of the overtravel stops of FIG. 1.

FIG. 6 is a detailed view of one of the overtravel stops and backplate of FIG. 1.

FIG. 7 is an illustration of one of the overtravel stops and a spring of the membrane of FIG. 1.

FIG. 8 is a perspective view of the overtravel stop of FIG. 1.

FIG. 9 is another embodiment of a MEMS microphone including four overtravel stops.

FIG. 10 is yet another embodiment of a MEMS microphone including a noncircular membrane.

DETAILED DESCRIPTION

Before any embodiments of the disclosure are explained in detail, it is to be understood that the disclosure is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The disclosure is capable of other embodiments and of being practiced or of being carried out in various ways.
A MEMS microphone is designed to convert acoustic pressure into an electrical signal. The MEMS microphone senses the acoustic pressure with a movable membrane connected with springs within a MEMS microphone die. The membrane is biased with a voltage. When the membrane moves relative to a backplate, capacitance between the membrane and the backplate varies in proportion to the amount of movement. The MEMS microphone generates the electrical signal based on the capacitive changes and thus varies the electrical signal based on the intensity of the acoustic pressure received at a membrane.
Based on the acoustic pressure, the membrane experiences acceleration in an axial direction (i.e., the direction of applied acoustic pressure). If the acoustic pressure is large enough, the acceleration may exceed the restorative force of the springs. In this case, the MEMS microphone may be damaged. In addition, external movements and impacts can result in excessive acceleration of the membrane in multiple directions. For example, dropping the MEMS microphone against a hard surface may result in a rapid acceleration on impact. Equipping the MEMS microphone with a plurality of overtravel stops (OTS), as disclosed herein, helps protect the membrane from excessive acceleration. The OTS helps prevent the membrane from travelling out of a safe range of movement in multiple directions.
FIG. 1 illustrates an internal view of a MEMS microphone 100. The MEMS microphone 100 includes a membrane 105, a backplate 110, and a plurality of overtravel stops (OTS 115). In the exemplary illustration, the membrane 105 is positioned below the backplate 110 and visible through the backplate 110. The membrane 105 is a movable structure (e.g., a diaphragm) within the MEMS microphone 100. An oxide anchor 120 is physically attached to the backplate 110, which is a rigid structure. In addition, the oxide anchor 120 is physically attached to the membrane 105. Thus, the oxide anchor 120 provides a mechanical connection point between the membrane 105 and the backplate 110. The oxide anchor 120 is formed of a nonconductive metal oxide that also provides electrical isolation between the membrane 105 and the backplate 110. Due to the electrical isolation, the membrane can be biased at a different potential than the backplate 110. Also illustrated in FIG. 1 are electrical connection pads 125. The electrical connection pads 125 provide a source of electrical potential for both the backplate 110 and the membrane 105.
FIG. 2 illustrates the membrane 105. The membrane 105 is made of a contiguous layer of material that allows flexibility in an axial direction. On the perimeter of the membrane 105 are a plurality of springs 205 that are formed out of the membrane 105 by creating thin slits 210 between portions of the membrane 105. FIG. 3 is a detailed view of one of the plurality of springs 205 on the perimeter of the membrane 105. Each of the springs 205 includes a thin beam 305 of material between the thin slits 210 that extends along the perimeter of the membrane 105 and to a surface 310. The surface 310 attaches to the oxide anchor 120. The surface 310 is fixed relative to the backplate 110. The thin beam 305 allows the membrane 105 to flex relative to the surface 310.
FIG. 4 illustrates an embodiment of a backplate layer 405. The backplate layer 405 includes the backplate 110 and the OTS 115. The backplate 110 includes a honeycomb surface 410 that allows acoustic pressure to enter the MEMS microphone 100. In such an embodiment, twenty-two OTS 115 are positioned along the perimeter of the backplate 110. The OTS 115 are released from the backplate layer 405 during the manufacturing process. It should be noted that in some embodiments there are more or less OTS 115.
FIG. 5 illustrates a detailed view of an embodiment of a single OTS 515. The OTS 515 has a first end 510 orientated proximal to the membrane 105 and a second end 512 orientated distal to the membrane 105. The first end 510 and the second end 512 are connected by a portion of the OTS 515. In this embodiment, the second end 512 flares outward as compared to the first end 510 thus resulting in a roughly bottle-shaped or vase-shaped OTS 515. The second end 512 has an arch-shaped stop 517 on each side of the second end 512 that provide contact points with the backplate layer 405. Each arch-shaped stop 517 is roughly perpendicular to a radial direction of the membrane 105.
The OTS 515 is physically separated from the backplate layer 405 by etching or otherwise removing material from the backplate layer 405 surrounding the OTS 515. The separation is illustrated as a gap 520. The gap 520 is generally a straight cut thus forming the OTS 515 with flat sides. The gap 520 sets a predetermined distance that the OTS 515 may travel before the OTS 515 restricts movement of the membrane 105. A connection point 525 physically attaches a bottom side of the first end 510 of the OTS 515 with the membrane 105. It should be noted that the OTS 515 may have alternative shapes.
FIG. 6 illustrates an embodiment of the OTS 515 positioned on the backplate layer 405. As illustrated, the gap 520 provides a small clearance between the OTS 515 and the backplate layer 405. The gap 520 is formed by cutting through the backplate layer 405 that effectively isolates a portion of the backplate layer 405 to form the OTS 515. When the membrane 105 is actuated by acoustic pressure, the gap 520 provides clearance for movement of the OTS 515 and the membrane 105. However, once the membrane 105 reaches its maximum deflection, the OTS 515 contacts the backplate layer 405. Since the OTS 515 is connected to the membrane 105 via the connection point 525 the membrane 105 is prevented from excessive deflection (i.e., overtravel). In particular, the second end 512 of the OTS 515 is configured to contact the backplate layer 405 when the movement of the membrane 105 has reached its safe maximum displacement. However, it should be noted that the OTS 515 may contact the backplate layer 405 at a plurality of contact points 605 including at the first end 510 of the OTS 515 or along the sides of the OTS 515. The contact points 605 provide structural and radial support for the OTS 515. Additionally, the contact points 605 may provide support in other directions. For example, the contact points 605 may restrict movement of the OTS 515 in a circumferential direction. By restricting movement of the OTS 515, the membrane 105 is also restricted in its movement range. In particular, acoustic pressure imparts force in an axial direction of the membrane 105. This force in the axial direction causes some radial movement of the OTS 515. This is because the membrane 105 pulls on the OTS 515 toward the center of the membrane 105 as the membrane 105 extends in either axial direction.
FIG. 7 illustrates an embodiment of an exemplary position of the OTS 515 relative to the membrane 105. The OTS 515 is positioned along an inside curve 705 of the perimeter of the membrane 105. The OTS 515 is affixed to the membrane 105 at the connection point 525. Other than the connection point 525, the OTS 515 is detached and positioned above the membrane 105, the springs 205, and the surface 310. The OTS 515, even though formed on the same layer as the backplate 110, the OTS 515 is physically separate and mechanically isolated from the backplate 110.
FIG. 8 illustrates a perspective view of the OTS 515. In order to illustrate the relationship of the OTS 515 with the membrane 105, the OTS 515 is illustrated with the backplate layer 405 removed. As illustrated, the membrane 105 is positioned under the OTS 515 and connected to the connection point 525 of the first end 510 of the OTS 515. The oxide anchor 120 provides a thin connection point between the backplate layer 405 and the surface 310. As a consequence, the membrane 105 is connected via the springs 205 to the oxide anchor 120, and the oxide anchor 120 is connected to the backplate 110. As illustrated, the backplate 110 is connected at a top of the oxide anchor 120 such that the backplate layer 405 surrounds the OTS 515. As the OTS 515 is formed from the backplate layer 405, the OTS 515 has the same thickness as the backplate layer 405.
FIG. 9 illustrates another embodiment of the MEMS microphone 100. In the exemplary illustration, four OTS 915 are positioned around the perimeter of the membrane 905. It should be noted that the number of OTS 915 may vary with each implementation. However, increasing the number of OTS 915 tends to provide more uniform support for the membrane 905. Another embodiment is illustrated in FIG. 10. Such an embodiment includes a non-circular membrane 1005 and OTS 1015. In the particular example, the membrane 1005 is square-shaped. Various other membrane shapes and styles are possible without departing from the spirit of the disclosure.
Thus, the disclosure provides, among other things, a MEMS microphone 100 with a plurality of OTS 515 located on a backplate layer 405. The OTS 515 are configured to restrict movement of the membrane 105 in multiple directions including in the radial direction of the membrane. Each of the OTS 515 provides contact points 605 that contact the backplate 110 when the membrane has reached its maximum safe deflection. Various features and advantages of the disclosure are set forth in the following claims.

Claims

What is claimed is:

1. A MEMS microphone comprising:

a membrane coupled to a support; and

a layer including

a backplate coupled to the support, and

an overtravel stop coupled to the membrane and physically separated from the backplate by a gap in a radial direction, the overtravel stop having

a first end oriented proximal to the membrane, and

a second end oriented distal to the membrane and flaring outward to restrict movement of the membrane in the radial direction by contacting the backplate.

2. The MEMS microphone of claim 1, wherein the second end of the overtravel stop has an arch-shaped stop on each side of the second end of the overtravel stop, the arch-shaped stop being perpendicular to the radial direction.

3. The MEMS microphone of claim 2, wherein the two arch-shaped stops contact the backplate when the membrane has reached a maximum deflection.

4. The MEMS microphone of claim 1, wherein the first end of the overtravel stop is coupled to the membrane.

5. The MEMS microphone of claim 1, wherein the overtravel stop is located along a perimeter of the membrane.

6. The MEMS microphone of claim 1, wherein the support includes an oxide anchor.

7. The MEMS microphone of claim 1, wherein the second end of the overtravel stop flares outward to restrict movement of the membrane in an inward radial direction by contacting the backplate.

8. The MEMS microphone of claim 1, wherein the membrane is coupled to the support via a spring.

9. The MEMS microphone of claim 8, wherein the spring is formed out of the membrane.

10. The MEMS microphone of claim 1, wherein the overtravel stop is released from the backplate.

11. A MEMS device comprising:

a movable structure coupled to a support; and

a layer including

a rigid structure coupled to the support, and

an overtravel stop coupled to the movable structure and physically separated from the rigid structure by a gap in a radial direction, the overtravel stop having a first end oriented proximal to the movable structure, and

a second end oriented distal to the movable structure and flaring outward to restrict movement of the movable structure in the radial direction by contacting the rigid structure.

12. The MEMS device of claim 11, wherein the second end of the overtravel stop has an arch-shaped stop on each side of the second end of the overtravel stop, the arch-shaped stop being perpendicular to the radial direction.

13. The MEMS device of claim 12, wherein the arch-shaped stops contact the rigid structure when the movable structure has reached a maximum deflection.

14. The MEMS device of claim 11, wherein the first end of the overtravel stop is coupled to the movable structure.

15. The MEMS device of claim 11, wherein the overtravel stop is located along a perimeter of the movable structure.

16. The MEMS device of claim 11, wherein the support includes an oxide anchor.

17. The MEMS device of claim 11, wherein the second end of the overtravel stop flares outward to restrict movement of the movable structure in an inward radial direction by contacting the rigid structure.

18. The MEMS device of claim 11, wherein the movable structure is coupled to the support via a spring.

19. The MEMS device of claim 18, wherein the spring is formed out of the movable structure.

20. The MEMS device of claim 11, wherein the overtravel stop is released from the rigid structure.