MINIATURE NON-DIRECTIONAL MICROPHONE

• US 20080101641A1
• Filed: 10/18/2006
• Published: 05/01/2008
• Est. Priority Date: 10/18/2006
• Status: Active Grant

• Current Assignee: The Research Foundation for The State University of New York (State University of New York)
• Original Assignee: The Research Foundation for The State University of New York (State University of New York)
• Inventors: Miles, Ronald N.
• Granted Patent: US 7,903,835 B2
• Time in Patent Office: Days
• US Class Current: 381/355
• CPC Class Codes: H04R 23/006 using solid state devices solid state devices per se H01L

Abstract

A miniature microphone comprising a diaphragm compliantly suspended over an enclosed air volume having a vent port is provided, wherein an effective stiffness of the diaphragm with respect to displacement by acoustic vibrations is controlled principally by the enclosed air volume and the port. The microphone may be formed using silicon microfabrication techniques and has sensitivity to sound pressure substantially unrelated to the size of the diaphragm over a broad range of realistic sizes. The diaphragm is rotatively suspend for movement through an arc in response to acoustic vibrations, for example by beams or tabs, and has a surrounding perimeter slit separating the diaphragm from its support structure. The air volume behind the diaphragm provides a restoring spring force for the diaphragm. The microphone'"'"'s sensitivity is related to the air volume, perimeter slit, and stiffness of the diaphragm and its mechanical supports, and not the area of the diaphragm.

Claims

1. A microphone, comprising:

a) a housing defining at least sidewalls of an enclosed volume region;

b) a diaphragm displaceably supported adjacent to the housing to form at least a portion of an enclosure for the volume region; and

c) at least one venting region, for equalizing a pressure in the volume region with an environment,

wherein a change in volume of a fluid or gas in the volume region induced by a displacement of the diaphragm provides substantially all of a restoring force opposing movement of the diaphragm in response to acoustic pressure waves.

2. The microphone according to claim 1, wherein the housing comprises a perforated substrate and a cover, the diaphragm, perforated substrate and cover substantially enclosing the volume region.

3. The microphone according to claim 1, wherein the diaphragm comprises a micromachined silicon membrane.

4. The microphone according to claim 1, wherein the vent comprises a gap disposed between at least a portion of a perimeter of the diaphragm and a wall of the housing.

5. The microphone according to claim 1, wherein the vent conducts a viscous flow of fluid therethrough in response to acoustic vibration induced displacement of the diaphragm.

6. The microphone according to claim 1, whereby a sensitivity of the microphone at an acoustic frequency is principally determined by a volume of air within the volume region.

7. The microphone according to claim 1, further comprising at least one torsional support for displaceably supporting the diaphragm adjacent to the volume region.

8. The microphone according to claim 1, further comprising at least one flexural support for displaceably supporting the diaphragm adjacent to the volume region.

9. The microphone according to claim 1, wherein the diaphragm deflects about a rotational axis in response to acoustic waves.

10. The microphone according to claim 1, further comprising a transducer for converting a displacement of the diaphragm into an electrical signal.

11. The microphone according to claim 1, further comprising an interdigital transducer for detecting a displacement of the diaphragm.

12. The microphone according to claim 1, further comprising an optical transducer for detecting a displacement of the diaphragm.

13. The microphone according to claim 1, wherein a diaphragm response is approximated by a linear second order oscillator model:

m{umlaut over (x)}+kx+C{dot over (x)}=−

PA 

 

(1)

where m is a mass of the diaphragm, x is a displacement of the diaphragm, k is an effective mechanical stiffness of the diaphragm, C is the viscous damping coefficient of a fluid flowing through the vent, and P is the pressure incident on the diaphragm due to an applied sound field, wherein k is defined principally by a volume of air in the volume region.

14. A method of forming a microphone comprising:

a) providing a substrate;

b) depositing a sacrificial layer on an upper surface of the substrate;

c) depositing a layer of structural material on an upper surface of the sacrificial layer to form a diaphragm layer;

d) creating at least one gap in the layer of structural material to isolate a microphone diaphragm region from peripheral region;

e) creating a void volume in the substrate below the microphone diaphragm region; and

f) removing a portion of the sacrificial layer.

15. The method according to claim 14, wherein the substrate comprises a silicon wafer.

16. The method according to claim 14, wherein the at least one gap is created by an etching process.

17. The method according to claim 14, wherein the structural material comprises polysilicon.

18. The method according to claim 14, wherein the void is created by performing a backside etch on the structural wafer.

19. A miniature, non-directional microphone manufactured using silicon microfabrication techniques and having a stiff silicon diaphragm supported by at least one beam, said microphone having at least one of a sensitivity and a low frequency response unrelated to a dimension of said diaphragm.

20. A microphone, comprising:

a) a stiff diaphragm;

b) a resilient support for said diaphragm, said support being adapted to permit said diaphragm to freely respond to acoustic waves by displacement thereof;

c) a housing defining, with the diaphragm, a region having a volume comprising at least a space behind the diaphragm, wherein a displacement of said diaphragm changes a volume of the region;

d) at least one port, communicating between the region and an environment,

wherein a responsivity of said diaphragm to displacement by acoustic waves in an audio range is principally defined by a volume of the region and a configuration of the at least one port.