Fatigue in Nanometric Single-Crystal Silicon Layers and Beams

This paper extends the experimental evidences of fatigue in micrometric structural silicon, typical of microelectromechanical systems processes, down to the submicrometric scale. The rationale lies in two naïve considerations. Fatigue is not observed at the macroscale, but becomes evident at the microscale. Thus, it should occur even more evidently at the nanoscale, where critical crack lengths decrease and if it becomes more evident, it may allow a deeper insight on the still debated origin of this phenomenon. Two suitable test structures, including 250-nm-thick notches and beams, are designed, fabricated, and subject to a fatigue campaign. Results on 34 samples show failures within a few minutes (at 20 kHz) for applied stresses as low as 38% of the measured nominal strength.