Strength and Fracture of Micromachined Silicon Structures

We present our recent efforts to understand and characterize the mechanical behavior of micromachined single crystal silicon structures. This includes efforts directed toward the design and fabrication of free-standing thin film test structures and toward micromechanical tensile testing. We observed that in many cases, fracture of the test structures initiates at sharp corners that arise from the anisotropic wet etching process. Existing approaches do not appear to be suitable to correlate fracture initiation from these sharp corners. To remedy this, we propose a new approach that is able to describe the apparent strength scaling with specimen size that is observed experimentally. This scaling has obvious ramifications with regard to the design of reliable structures for microelectromechanical systems, without exhaustive verification testing.