Specimen size effect on mechanical properties of polysilicon microcantilever beams measured by deflection using a nanoindenter

The validity of a novel, direct and convenient method for micromechanical property measurements by beam bending using a nanoindenter has been demonstrated. In the deflection of microbeams, the influence of the indenter tip pushing into the top of the microbeams and the curvature across its width must be considered. The elastic deflection of a polysilicon microcantilever beam will vary linearly with the force. Thus, Youngʹs modulus of the beam determined from the slope of this linear relation is 156 Gpa±2.9–6.3%. The size effects of the manufactured component on Youngʹs modulus and strength of polysilicon microcantilever beams were measured. This result shows that the rupture strengths of polysilicon beams show size effect on the effective volume and surface area of the specimens. The rupture strength of each sample decreased with increasing the specimen effective volume and surface area, but increased with increasing the surface-to-volume ratio. The defect that initiates fracture is often on the surface of the specimen. In such cases the size effect can be traced back to a surface-to-volume ratio as the governing parameter.