MEMS device and process
The application describes a MEMS transducer comprising a layer of conductive material provided on a surface of a layer of membrane material. The layer of conductive material comprises first and second regions, wherein the thickness and/or the conductivity of the/each first and second regions is different.
1. A MEMS transducer comprising
a substrate having a cavity;
a layer of membrane material provided relative to the substrate, wherein the membrane material extends over the cavity; and
a layer of conductive material provided on a surface of the layer of membrane material;
the layer of conductive material comprising at least one first region having a first thickness and a first conductivity and at least one second region having a second thickness and a second conductivity, wherein the thickness and/or the conductivity of the/each first and second regions is different and wherein at least one second region of the conductive material is provided on a region of the surface of the layer of membrane material which is laterally outside the region of the layer of membrane material which overlies the cavity.
2. A MEMS transducer as claimed in claim 1 , wherein the first region and the second region of the conductive material exhibit different thicknesses.
3. A MEMS transducer as claimed in claim 1 , wherein the first and second regions form an electrically continuous conductive layer on the surface of the membrane.
4. A MEMS transducer as claimed in claim 1 , wherein the second region of the layer of conductive material comprises first and second sub-layers of conductive material.
5. A MEMS transducer as claimed in claim 4 , wherein at least one of the sub-layers comprises a layer of conductive material having at least one opening.
6. A MEMS transducer as claimed in claim 1 , wherein at least one first region is provided on a region of the membrane which overlies the substrate cavity.
7. A MEMS transducer as claimed in claim 1 , wherein the conductive material forming the first region comprises a continuous sheet of conductive material.
8. A MEMS transducer as claimed in claim 1 , wherein the conductive material forming the first region comprises a layer of conductive material having at least one opening.
9. A MEMS transducer as claimed in claim 1 , wherein the layer of conductive material forms a membrane electrode of the transducer.
10. A MEMS transducer as claimed in claim 9 , wherein the layer of conductive material forms a conductive track which extends between the membrane electrode and a region for electrically coupling said membrane electrode to circuitry for readout.
11. A MEMS transducer as claimed in claim 10 , wherein the track is at least partially formed of at least one second region.
12. A MEMS transducer as claimed in claim 1 , wherein the layer of membrane material exhibits at least one step between a first level and a second level, and wherein at least one second region is provided on a region the layer of membrane material which includes said step.
13. A MEMS transducer as claimed in claim 1 , wherein the second region comprises one or more elements or interconnected tracks which are provided on a region of the layer of membrane material which overlies the cavity.
14. A MEMS transducer as claimed in claim 1 , wherein the first region and the second region of the conductive material exhibit different electrical conductivity.
15. A MEMS transducer as claimed in claim 14 , wherein the first region exhibits a lower electrical conductivity than the second region.
16. A MEMS transducer as claimed in claim 15 , wherein the first region comprises a conductive dielectric material.
17. A MEMS transducer as claimed in claim 14 , wherein the second region comprises a metal material or a metal alloy material.
18. A MEMS transducer as claimed in claim 1 , wherein said membrane comprises a crystalline or polycrystalline material.
19. A MEMS transducer as claimed in claim 1 , wherein the conductive layer comprises three of more regions, each region having a different thickness and/or conductance to the other regions.
20. A MEMS transducer as claimed in claim 1 wherein said transducer comprises a capacitive sensor such as a capacitive microphone.
21. A MEMS transducer as claimed in claim 20 further comprising readout circuitry wherein the readout circuitry may comprise analogue and/or digital circuitry.
22. An electronic device comprising a MEMS transducer as claimed in claim 1 , wherein said device is at least one of: a portable device; a battery powered device; an audio device; a computing device; a communications device; a personal media player; a mobile telephone; a games device; and a voice controlled device.