Mems device and process

Abstract

This application relates to MEMS devices, especially MEMS capacitive transducers and to processes for forming such MEMS transducer that provide increased robustness and resilience to acoustic shock. The application describes a MEMS transducer (400) having at least one membrane layer (101) supported so as to define a flexible membrane. A strengthening layer (401; 701) is mechanically coupled to the membrane layer and is disposed around the majority of a peripheral area of the flexible membrane but does not extend over the whole flexible membrane. The strengthening layer, which in some embodiments may be formed from the same material as the membrane electrode (102) being disposed in the peripheral area helps reduce stress in membrane at locations that otherwise may be highly stressed in acoustic shock situations. The membrane may be supported over a substrate cavity and the strengthening layer may be provided in an area of the membrane that could make contact with the edge (202) of the substrate cavity.

1 .- 48 . (canceled) 
     
     
         49 . A MEMS transducer comprising:
 a substrate having a cavity;   a membrane layer comprising a flexible membrane suspended relative to the substrate; and   a strengthening layer disposed on said membrane layer in a region of contact at which the flexible membrane will contact an edge of the substrate cavity if sufficiently deflected.   
     
     
         50 . A MEMS transducer as claimed in  claim 49 , wherein the strengthening layer does not extend over the whole of the flexible membrane. 
     
     
         51 . A MEMS transducer as claimed in  claim 49 , wherein the strengthening layer extends radially inward from the region of contact towards the centre of the flexible membrane. 
     
     
         52 . A MEMS transducer as claimed in  claim 49 , wherein the strengthening layer extends radially outward from the region of contact away from the centre of the flexible membrane. 
     
     
         53 . A MEMS transducer as claimed in  claim 49 , wherein the strengthening layer extends both radially inward and radially outward about the region of contact but does not extend over the whole of the flexible membrane. 
     
     
         54 . A MEMS transducer as claimed  claim 49 , wherein the strengthening layer is disposed around the majority of a peripheral area of the flexible membrane including the region of contact and does not extend over the whole flexible membrane. 
     
     
         55 . A MEMS transducer as claimed in  claim 54 , wherein the perimeter of the opening of the substrate cavity comprises the region of contact. 
     
     
         56 . A MEMS transducer as claimed in  claim 49 , wherein the substrate cavity defines an opening over which the flexible membrane is suspended. 
     
     
         57 . A MEMS transducer as claimed in  claim 49  wherein the strengthening layer extends radially from a support structure supporting the membrane layer onto a flexible part of the membrane layer. 
     
     
         58 . A MEMS transducer as claimed in  claim 57  wherein the strengthening layer forms part of a side wall of the support structure. 
     
     
         59 . A MEMS transducer as claimed in  claim 49  wherein the strengthening layer comprises a layer of material which has at least one of: a greater elasticity; a greater plasticity and a greater ductility than the material of the membrane layer. 
     
     
         60 . A MEMS transducer as claimed in  claim 49  wherein the strengthening layer comprises a layer of material which is in greater tensile stress than the material of the membrane layer. 
     
     
         61 . A MEMS transducer as claimed in  claim 49  wherein the strengthening layer comprises a layer comprising at least one of the group of: titanium, aluminium, copper and gold or an alloy thereof. 
     
     
         62 . A MEMS transducer as claimed in  claim 49  wherein the strengthening layer comprises a plurality of layers of different materials having different materials characteristics. 
     
     
         63 . A MEMS transducer as claimed in  claim 49  wherein a first strengthening layer is coupled to the membrane layer in said peripheral area and the transducer further comprises a second strengthening layer having a different geometry on the membrane layer to the first strengthening layer. 
     
     
         64 . A MEMS transducer as claimed in  claim 49  wherein the membrane layer comprises a membrane electrode and wherein the strengthening layer is formed from the same material as the membrane electrode and wherein the material forming the membrane electrode is discrete from the strengthening layer disposed in the peripheral area of the membrane. 
     
     
         65 . A MEMS transducer as claimed in  claim 49  comprising a first area of first material disposed so as to form a membrane electrode and a second area of first material disposed to form said strengthening layer wherein said second area substantially surrounds said first area wherein between the first and second areas there is a third area which is mainly devoid of any first material. 
     
     
         66 . A MEMS transducer as claimed in  claim 49  wherein the membrane layer is supported above a substrate and the strengthening layer is disposed on the opposite side of the membrane layer to the substrate. 
     
     
         67 . A MEMS transducer as claimed in  claim 49  wherein the strengthening layer extends from a peripheral area of the flexible membrane to at least 50 μm past the point of contact. 
     
     
         68 . A MEMS transducer as claimed in  claim 49  wherein said transducer comprises a microphone. 
     
     
         69 . An electronic device comprising a MEMS transducer as claimed in  claim 49  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. 
     
     
         70 . A MEMS transducer comprising:
 a flexible membrane suspended over a first surface of a substrate,   the substrate having one or more substrate cavities, the one or more substrate cavities defining an opening area in the first surface;   wherein a peripheral area of the suspended membrane carries a strengthening layer, the strengthening layer overlying the perimeter of the opening area; and   a non-peripheral area of the surface of the membrane is devoid of the material of the strengthening layer.   
     
     
         71 . A MEMS transducer as claimed in  claim 71 , wherein, when considering a cross-section taken across a width of the membrane, the strengthening layer is provided at a point of contact at which the which the flexible membrane will contact an edge of the substrate cavity if sufficiently deflected.