Fatigue studies of nanoscale structures for MEMS/NEMS applications using nanoindentation techniques

Mechanical properties of nanoscale structures are needed to design reliable micro/nanoelectromechanical systems (MEMS/ NEMS). Most material properties are known to be size-dependent and such properties of the nanoscale structures have not been well characterized. Bending strength and fatigue properties of nanoscale silicon beams with a 6-mum length, a 255 nm height and widths ranging from 400 to 800 nm were evaluated using a depth-sensing nanoindenter with a harmonic force. In the bending tests, the beams failed in a brittle manner with a flat fracture surface. Load cycles used in continuous stiffness measurement were used to perform fatigue tests. The contact stiffness was monitored continuously throughout the fatigue test. The abrupt decrease in the contact stiffness indicates fatigue damage has occurred. Cleavage steps were found on the fatigue fracture surface. Failure mechanisms of the beams during bending and fatigue are also discussed in conjunction with the surface to volume ratio, surface defects, and cleavage planes. The dynamic nanoindentation fatigue test used in this study can be satisfactorily used to evaluate the fatigue behavior of nanoscale structures for use in MEMS/NEMS. (C) 2002 Elsevier Science B.V. All rights reserved.