Mems device and process

Abstract

The application describes improvements to (MEMS) transducers ( 100 ) having a flexible membrane ( 301 ) with a membrane electrode ( 302 ), especially where the membrane is crystalline or polycrystalline and the membrane electrode is metal or a metal alloy. Such transducers may typically include a back-plate having at least one back-plate layer ( 304 ) coupled to a back-plate electrode ( 303 ), with a plurality of holes ( 314 ) in the back-plate electrode corresponding to a plurality back-plate holes ( 312 ) through the back-plate. In embodiments of the invention the membrane electrode has at least one opening ( 313 ) in the membrane electrode wherein, at least part of the area of the opening corresponds to the area of at least one back-plate hole, in a direction normal to the membrane, and there is no hole in the flexible membrane at said opening in the membrane electrode. There may be a plurality of such openings. The openings effectively allow a reduction in the amount of membrane electrode material, e.g. metal, that may undergo plastic deformation and permanently deform the membrane. The openings are at least partly aligned with the back-plate holes to minimise any loss of capacitance.

1 .- 42 . (canceled) 
     
     
         43 . A MEMS transducer comprising:
 a membrane electrode provided with at least one opening; and   a backplate electrode provided with at least one hole;   
       wherein, when a backplate hole is projected onto the plane of the membrane electrode in a direction normal to the backplate electrode,
 a) an area of the hole is within an area of the corresponding opening in the membrane electrode; or 
 b) an area of the corresponding opening in the membrane electrode is within an area of the hole. 
 
     
     
         44 . The MEMS transducer as claimed in  claim 43 , wherein the MEMS transducer comprises a flexible membrane to which the membrane electrode is coupled. 
     
     
         45 . The MEMS transducer as claimed in  claim 43 , wherein the MEMS transducer comprises a backplate, wherein the backplate electrode is supported by the backplate. 
     
     
         46 . The MEMS transducer as claimed in  claim 45 , wherein the holes in the backplate electrode correspond to a plurality of backplate holes through the backplate. 
     
     
         47 . The MEMS transducer as claimed in  claim 43  wherein said flexible membrane comprises a crystalline or polycrystalline material. 
     
     
         48 . The MEMS transducer as claimed in  claim 47  wherein said flexible membrane comprises silicon nitride. 
     
     
         49 . The MEMS transducer as claimed in  claim 47  wherein said flexible membrane has intrinsic stress. 
     
     
         50 . The MEMS transducer as claimed in  claim 43  wherein said membrane electrode comprises metal or a metal alloy, such as aluminium. 
     
     
         51 . The MEMS transducer as claimed in  claim 43  wherein said at least some of said plurality of openings in the membrane electrode comprise a hole in said membrane electrode. 
     
     
         52 . The MEMS transducer as claimed in  claim 43  wherein the at least one opening in the membrane electrode extends from a lower surface of the membrane electrode to an upper surface of the membrane electrode. 
     
     
         53 . The MEMS transducer as claimed in  claim 43  wherein at least one of said at least one opening in the membrane electrode are substantially the same shape as at least one of said at least one hole in the back-plate electrode. 
     
     
         54 . The MEMS transducer as claimed in  claim 44  wherein said the distribution of said at least one opening in the membrane electrode is configured to provide even stress as the membrane flexes. 
     
     
         55 . The MEMS transducer as claimed in  claim 44  wherein less than 20% of the stress in the flexible membrane-membrane electrode structure is due to said flexible membrane. 
     
     
         56 . The MEMS transducer as claimed in  claim 44  wherein less than 25% of the surface area of said flexible membrane is covered by electrode material. 
     
     
         57 . The MEMS transducer as claimed in  claim 44  wherein the outer perimeter of the electrode encloses an area of membrane greater than 35% of the area of said membrane. 
     
     
         58 . The MEMS transducer as claimed in  claim 43  wherein said MEMS transducer is a microphone. 
     
     
         59 . An audio device comprising a MEMS transducer as claimed in  claim 43  wherein said device is at least one of: a portable device; a communications device; a computing device; a battery powered device; an audio player; a video player; a gaming device; a mobile telephone; a laptop, notebook or tablet computer. 
     
     
         60 . A MEMS transducer comprising:
 a membrane electrode provided with at least one opening; and   a back-plate electrode provided with at least one hole; wherein
 each hole in the back-plate electrode at least partially overlies a corresponding opening in the membrane electrode, and wherein a first width of a respective hole in the back-plate electrode is smaller than a second width of the corresponding opening in the membrane electrode or vice versa. 
   
     
     
         61 . The MEMS transducer as claimed in  claim 60  wherein the first width of the respective hole differs from the second width of the corresponding opening by up to 2 microns.