MEMS process and device

1. A micro-electrical-mechanical system (MEMS) package, comprising:

a package substrate; and

a MEMS capacitive microphone situated on the package substrate within the MEMS package;

wherein the MEMS capacitive microphone comprises:

a substrate;

a membrane formed relative to a first side of the substrate; and

a back-volume formed in the substrate relative to a second side of the substrate;

wherein the back-volume comprises a first back-volume portion and a second back-volume portion having a boundary therebetween defined by a discontinuity in a sidewall of the substrate; and

wherein the cross sectional area of the second back-volume portion is greater than the cross sectional area of the first back-volume portion.

2. A MEMS package as claimed in claim 1 , wherein the discontinuity comprises a discontinuity in the cross-sectional area of the back volume in a plane parallel to the substrate.

3. A MEMS package as claimed in claim 1 , wherein the discontinuity comprises a discontinuity in a rate of change of cross-sectional area of the back volume in a plane parallel to the substrate with distance from the membrane.

4. A MEMS package as claimed in claim 1 , wherein the discontinuity is curved.

5. A MEMS package as claimed in claim 1 , wherein the discontinuity comprises a change in the gradient of the sidewall.

6. A MEMS package as claimed in claim 1 , wherein the discontinuity comprises two or more changes in the gradient of the sidewall.

7. A MEMS package as claimed in claim 1 , wherein the first back-volume portion has a cross-sectional area that is smaller than the cross-sectional area of the membrane in a plane where the first back-volume portion and the membrane meet.

8. A MEMS package as claimed in claim 1 , wherein the cross-sectional area of the second back-volume portion is greater than the cross-sectional area of the membrane.

9. A MEMS package as claimed in claim 1 , wherein the first back-volume portion has sloped walls.

10. A MEMS package as claimed in claim 1 , wherein the second back-volume portion has sloped sidewalls.

11. A MEMS package as claimed in claim 1 , wherein the acoustic back-volume further comprises a third back-volume portion.

12. A MEMS package as claimed in claim 11 , wherein the third back-volume portion is positioned between the first back-volume portion and the membrane.

13. A MEMS package as claimed in claim 11 , wherein the third back-volume portion has a cross sectional area or diameter that is larger than the cross-sectional area or diameter of the first back-volume portion.

14. A MEMS package as claimed in claim 1 , wherein the first back-volume portion borders with the first side of the substrate and the second back-volume portion borders with the second side of the substrate.

15. A MEMS package as claimed in claim 1 , wherein the discontinuity comprises a kink in the sidewall of the back-volume.

16. A MEMS package as claimed in claim 1 , wherein the discontinuity comprises a step in the sidewall of the back-volume.

17. A MEMS package as claimed in claim 16 , wherein the step comprises substantially a right angled step in the sidewall of the back-volume.

18. A MEMS package as claimed in claim 1 , wherein the shape of an opening of the second back-volume portion is similar in shape to the substrate of the MEMS capacitive microphone.

19. A MEMS package as claimed in claim 18 , wherein the opening of the second back-volume portion and the substrate are circular in shape, or rectangular in shape, or square in shape.

20. A MEMS package as claimed in claim 1 , wherein the shape of an opening of the first back-volume portion is similar in shape to the membrane of the MEMS capacitive microphone.

21. A MEMS package as claimed in claim 20 , wherein the opening of the first back-volume portion and the membrane are circular in shape, or rectangular in shape, or square in shape.

22. A MEMS package as claimed in claim 1 , wherein the shape of an opening of the first back-volume portion is matched to the shape of the membrane and/or wherein the shape of an opening of the second back-volume portion is matched to the shape of the substrate of the MEMS capacitive microphone.

23. A MEMS package as claimed in claim 1 , wherein the package substrate comprises a recess, and wherein the MEMS capacitive microphone is situated in said recess.

24. A MEMS package as claimed in claim 1 , wherein the package comprises a lid.

25. A MEMS package as claimed in claim 1 , wherein the package forms an RF cage.

26. A portable telephone device comprising a micro-electrical-mechanical system (MEMS) package as claimed in claim 1 .

27. A communications device comprising a micro-electrical-mechanical system (MEMS) package as claimed in claim 1 .

28. A computer device comprising a micro-electrical-mechanical system (MEMS) package as claimed in claim 1 .

29. A micro-electrical-mechanical system (MEMS) package, comprising:

a package substrate; and

a MEMS capacitive microphone situated within the MEMS package;

wherein the MEMS capacitive microphone comprises:

a substrate;

a membrane formed relative to a first side of the substrate; and

a back-volume comprising means for enabling the effective height of the MEMS capacitive microphone to be reduced for a given volume of back-volume.

30. A micro-electrical-mechanical system (MEMS) package, comprising:

a package substrate; and

a MEMS capacitive microphone situated within the MEMS package;

wherein the MEMS capacitive microphone comprises:

a substrate;

a membrane; and

a back-volume,

wherein the back-volume comprises first and second back-volume portions distinguishable by a discontinuity in a sidewall of the substrate; and

wherein the cross sectional area of the second back-volume portion is greater than the cross sectional area of the first back-volume portion.