Abstract
We present recent results regarding correlation of fracture initiation for i) micromachined epitaxial silicon structures, and ii) silicon/glass anodic bonds used for encapulation of microelectromechanical systems. Regarding the epitaxial silicon structures, we have previously correlated fracture initiation from the sharp notches that arise during anisotropic etching in KOH using a critical value of the stress intensity that exists in the context of linear elasticity. This has successfully explained an interesting strength scaling with structural dimensions. In this talk, we present new results along these lines where we have considered additional structure geometries (double-edge-notched silicon specimens, roughly 600 μm long × 50 μm wide × 15 μm thick), loadings (in-plane flexure), and etching processes (deep reactive ion etching). Regarding fracture initiation of silicon/glass anodic bonds, we have fabricated a series of generic test structures by anodically bonding etched silicon wafers to glass wafers. We have carried out preliminary tests in tensile and flexural loading and interpreted these results in the framework of an analysis of the singular stress state at the resulting bimaterial notch. For both cases, we will discuss the suitability of using critical stress intensities to correlate fracture initiation under the condition of small-scale inelastic effects.
