Deformation behaviour of polysilicon components for MEMS

The mechanical performance of miniaturized Si components depends on both microstructure and geometry. Nanoscale polysilicon beams with both fixed–fixed and portal–frame-type beam geometries have been experimentally deformed and modelled using FEA. It is shown here that the combination of both geometry of a beam support and nanoscale dimensions results in a significantly different mechanical response of beams to that predicted using bulk properties. In a fixed–fixed configuration, beams exhibit limited elasticity followed by rapid failure occurring at the beam mid-point. However, by allowing the beam to have a less rigid connection to the substrate as in the case for a portal–frame geometry, a beam of similar dimensions can undergo significantly more deformation (∼five times more), without failure. The increased flexibility of the support connection results in lower stresses particularly at critical positions along the beam and a lower maximum tensile stress of ∼35–40% less than for a fixed–fixed beam geometry. We also show that for cyclic deformation, a build-up in residual beam deformation is related to changes in microstructure, which can relax back to a less deformed state without continuously applied high deformation levels. (paper)