Microelectromechanical system devices having crack resistant membrane structures and methods for the fabrication thereof

A method for fabricating a Microelectromechanical (MEMS) device, the method comprising:

• forming a sense electrode on a substrate;
• depositing a sense dielectric layer over the sense electrode;
• forming a sacrificial body on the dielectric layer;
• building a multi-layer polysilicon membrane over the sacrificial body by forming multiple layers of polycrystalline silicon and planarizing at least one layer of polycrystalline silicon over which an additional layer of polycrystalline silicon is deposited such that at least the uppermost layer of the multi-layer polysilicon membrane is imparted with a substantially parallel grain structure;
• forming at least one channel through the multi-layer polysilicon membrane to the sacrificial body;
• removing at least a portion of the sacrificial body to form an inner cavity at least partially enclosed by the multi-layer polysilicon membrane;
• and
• forming a plug in the at least one channel to hermetically seal the inner cavity.

A Microelectromechanical (MEMS) device, comprising:

• a substrate;
• a multi-layer membrane structure formed on the substrate, the multi-layer membrane structure comprising:
• a base membrane layer, and
• a cap membrane layer formed over the base membrane layer, the cap membrane layer comprising a material having a substantially parallel grain orientation at the outer edge regions of the cap membrane layer;
• and
• a cavity at least partially enclosed by the multi-layer membrane structure.