Fracture testing of silicon microcantilever beams

Silicon microcantilever beams are fractured and characterized. The specially designed beams, etched into two wafers, are loaded to fracture in bending using a unique measurement system. A finite element model of the beams is created, and ABAQUS is used to calculate the displacements and stresses produced by an applied load force. A special testing scheme is devised to obtain certain model parameters: E[110], the Young's modulus along the length of the beam and L(force), the position of the applied force. With these parameters defined, the model is well correlated with that of the experimental data. The fracture stress (strength) of the beam is obtained from the stress produced in the model at the fracture location by a load equivalent to the experimental fracture force. This fracture stress can be used as a design parameter for silicon micromechanical structures. Numerous beams are fractured from both the front and back sides of the wafer, and statistical fracture strength results are compiled for each of these cases. The fracture strength of the front side, 3.3 GPa (average), is significantly greater than that of the backside, 1.0 GPa (average). This dissimilarity is attributed to the differences in the surface roughness of these sides. (C) 1996 American Institute of Physics.