Fatigue behavior of polysilicon nanowires.

Abstract

With advances in silicon microfabrication techniques, electromechanical sensors are shrunk to nanometer scale. Besides enhanced sensitivity, these nanoscaled sensors are found with improved electromechanical and thermoelectric property. Although the future of these devices is promising, the feasibility of having these nano-sensors integrated into commercial devices is unexplored. Here we focus on the mechanical reliability of silicon nanowires (SiNW) and the feastibility of these SiNWs for ultra-sensitive electromechanical sensor. SiNWs are embedded within the anchor of a micro-cantilever and undergo a micro-indentation test, where external cyclic loads are applied through a piezoelectric actuator at the free end of cantilever. This project proposed a technique to study the fatigue behavior of polycrystalline SiNWs through real-time electrical conductivity measurement of the SiNWs under cyclic load using a nano-testing device developed in our group.

Physical characterization of the SiNW was performed using SEM imaging. Finite element modeling using ANSYS was used to validate the theoretical response. Hyperbolic sine I- V characteristic of SiNW before and after 1 million cycles of stress loading was obtained. Fatigue behavior was observed by the 2.7% increase in resistance of the SiNW after 1 million cycles of stress loading, attributable to fatigue damage accumulation within the SiNW. The real time fatigue analysis results show that the maximum resistance of SiNW measured increases with the amount of cyclic stress applied on the SiNWs, possibly due to fatigue damage accumulation and hence mechanical deformation of SiNWs. Resistance for the SiNW under stress cycling at 1120 MPa had a sharp rise after 10 cycles, indicating failure of the SiO2 cantilever. SEM images of the fractured test specimen were taken, showing smooth fracture site on the SiO2 microcantilever.