MEMS device and process

A MEMS transducer comprising a flexible membrane with a vent structure 501 comprising at least one moveable portion 502 which, in response to differential pressure across the vent, deflects away from the plane of the membrane to reveal an aperture, wherein at least one edge of the moveable portion 502 has protrusions and/or recesses in the plane of the moveable portion. The flap may be separated from the diaphragm by a channel 502, the edges being interdigitated in a sinusoidal, square, triangle, serrated or saw-tooth shape. The vent bleed holes allow for pressure equalisation between cavities and the protrusions reduce the effect of high pressure impulses by providing an extended edge length thus preventing damage or overload of the diaphragm. The protrusion density may be varied, with a greater concentration at edges with the most deflection from the equilibrium position. A joint or beam may be between the triangular, rectangular, or square shaped membrane and flap 502. The microeletromechanical transducer may use capacitive sensing with electrodes and may be utilised as a microphone in mobile telephones, computing devices or other portable electronics.