Patent ID: 8921952

Claim:
A method for fabricating a Microelectromechanical (MEMS) device, the method comprising: forming a sacrificial body over a substrate; producing a multi-layer membrane structure on the substrate, wherein producing comprising: depositing polycrystalline silicon over and around the sacrificial body to form a base membrane layer having a non-planar upper surface, a stepped outer edge portion, and a region having a non-parallel grain orientation; removing a predetermined thickness of material from a top of the base membrane layer sufficient to eliminate the stepped outer edge portion, to remove atleast a portion of the region having the non-parallel grain orientation, and to impart the base membrane layer with a planar upper surface; and forming a cap membrane layer over the planar upper surface of the base membrane layer, the cap membrane layer comprising polycrystalline silicon having a substantially parallel grain orientation at the interface between the cap membrane layer and the base membrane layer; and removing at least a portion of the sacrificial body to form an inner cavity within the multi-layer membrane structure.