Optical microphone assembly
An optical microphone assembly including a micro-electromechanical system (MEMS) component, a semiconductor chip, and an outer housing including at least part of a non-MEMS supporting structure and defining an aperture. The MEMS component includes an interferometric arrangement which includes a membrane and at least one optical element spaced from the membrane. The semiconductor chip includes at least one photo detector and a light source. The MEMS component is mounted on the non-MEMS supporting structure and sealed to the outer housing such that the MEMS component closes the aperture. The semiconductor chip is mounted separately from the MEMS component on the non-MEMS supporting structure in a spaced relationship with the MEMS component such that the MEMS component is displaced relative to the semiconductor chip in a direction perpendicular to a reflecting surface of the membrane. The light source is arranged to provide light to the interferometric arrangement such that a first portion of the light propagates along a first optical path via the interferometric arrangement, and a second portion of the light propagates along a second, different optical path via the interferometric arrangement such that at least one of the first and second portions is reflected by the reflecting surface of the membrane, thereby giving rise to an optical path difference between the first and second optical paths which depends on a distance between the membrane and the optical element. The at least one photo detector is arranged to detect at least part of an interference pattern generated by the first and second portions of light dependent on the optical path difference.
1. An optical microphone assembly, comprising:
a micro-electromechanical system (MEMS) component comprising an interferometric arrangement, the interferometric arrangement comprising a membrane and at least one optical element spaced from the membrane;
a semiconductor chip comprising at least one photo detector;
a light source mounted on or integrated as part of the semiconductor chip;
a non-MEMS supporting structure; and
an outer housing including at least part of the non-MEMS supporting structure, the outer housing defining an aperture;
wherein the MEMS component is mounted on the non-MEMS supporting structure and sealed to the outer housing with the interferometric arrangement positioned between the light source and the aperture such that the MEMS component closes the aperture and does not create an acoustic cavity between the aperture and a side of the membrane that is in fluid communication with an exterior of the optical microphone assembly;
wherein the semiconductor chip is mounted separately from the MEMS component on the non-MEMS supporting structure in a spaced relationship with the MEMS component such that the MEMS component has a displacement relative to the semiconductor chip in a direction perpendicular to a reflecting surface of the membrane;
wherein the light source is arranged to provide light to the interferometric arrangement such that a first portion of said light propagates along a first optical path via said interferometric arrangement and a second portion of said light propagates along a second, different optical path via said interferometric arrangement such that at least one of said first and second portions is reflected by the reflecting surface of the membrane, thereby giving rise to an optical path difference between the first and second optical paths which depends on a distance between the membrane and the optical element; and
wherein the at least one photo detector is arranged to detect at least part of an interference pattern generated by said first and second portions of light dependent on said optical path difference.
2. The optical microphone assembly as claimed in claim 1 , wherein the aperture has a width or diameter at least as large as a width or diameter of the membrane.
3. The optical microphone assembly as claimed in claim 1 , wherein the width or diameter of the aperture is at least 500 μm.
4. The optical microphone assembly as claimed in claim 1 , wherein the aperture is flared such that the aperture has an inner width or diameter adjacent an interior of the optical microphone assembly and an outer width or diameter adjacent the exterior of the optical microphone assembly, wherein the outer width or diameter is larger than the inner width or diameter.
5. The optical microphone assembly as claimed in claim 1 , wherein the displacement of the MEMS component relative to the semiconductor chip in the direction perpendicular to the reflecting surface of the membrane is at least 250 μm.
6. The optical microphone assembly as claimed in claim 1 , wherein the non-MEMS supporting structure comprises:
a substrate;
a superstrate having the aperture formed therein; and
a spacer separating the substrate and the superstrate;
wherein the MEMS component is mounted on the superstrate to close the aperture and the semiconductor chip is mounted on the substrate facing the MEMS component.
7. The optical microphone assembly as claimed in claim 1 , wherein the non-MEMS supporting structure comprises:
a substrate having the aperture formed therein;
a superstrate; and
a spacer separating the substrate and the superstrate;
wherein the MEMS component is mounted on the substrate to close the aperture and the semiconductor chip is mounted on the superstrate facing the MEMS component.
8. The optical microphone assembly as claimed in claim 1 ,
wherein the non-MEMS supporting structure comprises a substrate defining a recess surrounded by a wall;
wherein the semiconductor chip is mounted in the recess and the MEMS component is mounted on top of the wall so as to span at least part of the recess;
wherein the optical microphone assembly further comprises an enclosure mounted on top of the wall so that the enclosure and the substrate together define an acoustic cavity; and
wherein the aperture is formed in the enclosure and the MEMS component is sealed to the enclosure such that the MEMS component closes the aperture.
9. The optical microphone assembly as claimed in claim 1 ,
wherein the non-MEMS supporting structure comprises a substrate defining a recess surrounded by a wall;
wherein the aperture is formed in the substrate and the MEMS component is mounted in the recess to close the aperture;
wherein the semiconductor chip is mounted on top of the wall so as to span at least part of the recess; and
wherein the optical microphone assembly further comprises an enclosure mounted on the substrate or on top of the wall so that the enclosure and the substrate together define an acoustic cavity.
10. The optical microphone assembly as claimed in claim 8 wherein the substrate is formed from a single piece such that the wall is an integrally formed part of the substrate.
11. The optical microphone assembly as claimed in claim 8 wherein the substrate is formed from a base piece and a spacer mounted thereon such that the spacer defines the wall.
12. The optical microphone assembly as claimed in claim 8 , wherein the semiconductor chip is mounted on top of the wall by bump bonding.
13. The optical microphone assembly as claimed in claim 1 , wherein the aperture is provided with a dust cover.
14. The optical microphone assembly as claimed in claim 1 , wherein the MEMS component together with the semiconductor chip defines an optical microphone, and wherein the optical microphone assembly comprises one or more further optical microphones on the non-MEMS supporting structure.
15. The optical microphone assembly as claimed in claim 9 , wherein the substrate is formed from a single piece such that the wall is an integrally formed part of the substrate.
16. The optical microphone assembly as claimed in claim 9 , wherein the substrate is formed from a base piece and a spacer mounted thereon such that the spacer defines the wall.
17. A method of manufacturing an optical microphone assembly, wherein the optical microphone assembly comprises:
a micro-electromechanical system (MEMS) component comprising an interferometric arrangement, the interferometric arrangement comprising a membrane and at least one optical element spaced from the membrane;
a semiconductor chip comprising at least one photo detector;
a light source mounted on or integrated as part of the semiconductor chip;
a non-MEMS supporting structure; and
an outer housing including at least part of the non-MEMS supporting structure, the outer housing defining an aperture;
the method comprising:
mounting the MEMS component on the non-MEMS supporting structure such that the MEMS component is sealed to the outer housing with the interferometric arrangement positioned between the light source and the aperture the MEMS component closes the aperture and does not create an acoustic cavity between the aperture and a side of the membrane that is in fluid communication with an exterior of the optical microphone assembly; and
mounting the semiconductor chip separately from the MEMS component on the non-MEMS supporting structure in a spaced relationship with the MEMS component such that the MEMS component has a displacement relative to the semiconductor chip in a direction perpendicular to a reflecting surface of the membrane; and
wherein mounting the semiconductor chip comprises positioning the semiconductor chip such that the light source is arranged to provide light to the interferometric arrangement such that a first portion of said light propagates along a first optical path via said interferometric arrangement and a second portion of said light propagates along a second, different optical path via said interferometric arrangement such that at least one of said first and second portions is reflected by the reflecting surface of the membrane, thereby giving rise to an optical path difference between the first and second optical paths which depends on a distance between the membrane and the optical element; and such that the at least one photo detector is arranged to detect at least part of an interference pattern generated by said first and second portions of light dependent on said optical path difference.