MEMS device and process
A MEMS capacitive transducer with increased robustness and resilience to acoustic shock. The transducer structure includes a flexible membrane supported between a first volume and a second volume, and at least one variable vent structure in communication with at least one of the first and second volumes. The variable vent structure includes at least one moveable portion which is moveable in response to a pressure differential across the moveable portion so as to vary the size of a flow path through the vent structure. The variable vent may be formed through the membrane and the moveable portion may be a part of the membrane, defined by one or more channels, that is deflectable away from the surface of the membrane. The variable vent is preferably closed in the normal range of pressure differentials but opens at high pressure differentials to provide more rapid equalization of the air volumes above and below the membrane.
1. A MEMS transducer comprising a flexible membrane supported between a substrate and a backplate, wherein the flexible membrane overlies a first cavity formed in the substrate,
wherein the transducer further comprises at least one port in the substrate which is in communication with the cavity and provides a flow path between the first cavity and a volume outside of the backplate, and
wherein a variable vent structure is provided in the flow path.
2. A MEMS transducer as claimed in claim 1 , wherein the variable vent structure is formed in a material layer of the transducer other than a material layer forming the flexible membrane.
3. A MEMS transducer as claimed in claim 1 , wherein the variable vent structure is formed in a material layer of the transducer that forms the flexible membrane.
4. A MEMS transducer as claimed in claim 1 , wherein the at least one port is provided outside the area of the flexible membrane.
5. A MEMS transducer as claimed in claim 1 , wherein the port extends through a material layer that forms the flexible membrane.
6. A MEMS transducer as claimed in claim 1 , wherein the port comprises first and second sections, the first section extends through the backplate and the second section extends through the substrate.
7. A MEMS transducer as claimed in claim 6 , wherein the first and second sections are separated by the variable vent structure.
8. A MEMS transducer as claimed in claim 1 wherein the backplate comprises at least one hole which extends through the backplate from a second cavity above the flexible membrane to the volume outside of the backplate, and wherein the port provides a flow path between the first cavity and the second cavity.
9. A MEMS transducer as claimed in claim 8 , wherein the flow path does not extend through the flexible membrane.
10. A MEMS transducer as claimed in claim 1 , wherein the variable vent structure comprises at least one moveable portion which is moveable in response to a pressure differential across the moveable portion so as to vary the size of the flow path through the vent structure.
11. A MEMS transducer as claimed in claim 1 , wherein the variable vent structure is formed in a layer provided within the flow path and comprises a moveable portion that is moveable in response to a pressure differential between the first cavity and the volume outside of the backplate so as to expose a hole in the layer, the moveable portion comprising a portion of the layer that is able to be deflected away from the surface of the rest of the layer.
12. A MEMS transducer as claimed in claim 1 , wherein the flow path extends through at least a part of a sidewall of said transducer structure.
13. A MEMS transducer comprising a flexible membrane supported relative to a substrate and extending above a first cavity in the substrate, the transducer further comprising a variable vent structure provided in a flow path between the first cavity and a volume above the flexible membrane, which flow path bypasses the flexible membrane.
14. A MEMS transducer as claimed in claim 13 , wherein the flow path comprises a port formed in the substrate that is in communication with said first cavity.
15. A MEMS transducer as claimed in claim 13 , wherein the variable vent structure is formed in a material layer of the transducer other than a material layer forming the flexible membrane.
16. A MEMS transducer as claimed in claim 13 , wherein the variable vent structure is a formed in a material layer of the transducer that forms the flexible membrane.
17. A MEMS transducer as claimed in claim 13 , wherein the variable vent structure comprises at least one moveable portion which is moveable in response to a pressure differential across the moveable portion so as to vary the size of the flow path through the vent structure.
18. A MEMS transducer as claimed in claim 1 , wherein the flow path extends through at least a part of a sidewall of said transducer structure.
19. A MEMS transducer comprising a flexible membrane supported between a first volume and a second volume and comprising a variable vent structure for varying the size of a flow path between the first volume and the second volume, wherein the flow path bypasses the membrane.
20. A MEMS transducer as claimed in claim 1 , wherein the variable vent structure comprises at least one moveable portion which is moveable in response to a pressure differential across the moveable portion so as to vary the size of the flow path through the vent structure.
21. A MEMS transducer comprising a flexible membrane supported between a first volume and a second volume, the transducer comprising a variable vent structure formed with a flow path between the first and second volumes that bypasses the flexible membrane.
22. A MEMS transducer as claimed in claim 21 , wherein the flow path extends through at least a part of a sidewall of the transducer.
23. A capacitive microphone comprising a MEMS transducer as claimed in claim 1 .
24. A capacitive microphone comprising a MEMS transducer as claimed in claim 13 .
25. A capacitive microphone comprising a MEMS transducer as claimed in claim 19 .
26. A capacitive microphone comprising a MEMS transducer as claimed in claim 21 .