Fracture testing of bulk silicon microcantilever beams subjected to a side load

A custom experimental system was developed to fracture silicon microcantilever beams in side loading (i.e., the load was applied in the noncompliant direction), and the resulting force/deflection (stiffness) characteristics were obtained. A finite element model of these structures was analyzed using ABAQUS, and the resulting model stiffness correlated well with the experimental data. Fracture types were divided into two categories, {111} and {110}, according to the type of silicon crystalline plane along which fracture occurred. The initiation location of each fracture type was identified. The fracture stress (strength) in the beam was obtained from the stress produced in the model at the fracture initiation site for a load equivalent to the experimental fracture force. Numerous beams were tested, and the statistical results were compiled. The distributions and statistical data from each of the fracture types were compared to each other and to previously acquired results from front/back loading (i.e., loading in the compliant direction) of these same structures. Side-loading results indicated that the {110} fracture type had a greater fracture strength than the {111} type. Based on a comparison of the side loading data with the front/back loading data, it was concluded that side wall roughness and especially the edge roughness greatly affected the fracture strength of the silicon micromechanical structures.