On the Fracture Toughness of Polysilicon MEMS Structures

摘要

The mechanical properties of micromachined polysilicon are of great interest to designers of microelectromechanical systems (MEMS) devices. Numerous investigations have been carried out to determine the strength of MEMS-fabricated polysilicon structures, and the experimental results vary widely, depending on the experimental techniques, specimen geometries, and processing conditions. In order to determine whether these variations are inherent to all mechanical properties of MEMS materials, the fracture toughness, K_(crit), of micromachined polysilicon has been investigated, using a wide range of material microstructures (microstructure is used here in the Materials Science sense to mean the grain structure visible in a microscope, and not in the MEMS sense to mean small structures). Since fracture toughness is a fundamental materials property, whether or not it varies with microstructure and processing is an interesting question. We have confirmed that K_(crit) is not a microstructure-sensitive property, using surface-micromachined specimens with sharp pre-cracks which are integrated with electrostatic actuators. The measured K_(crit) is 1.0+-0.1 MPa√m for a wide range of microstructures.