Effects of coating materials on two dimensional stress-induced deflection of nanomechanical sensors.

Nanomechanical sensors, which have been expected as a promising platform for various applications, will not generate any measureable signal without an appropriate coating (receptor) layer. In spite of this critical dependence on the coating layer, there is almost no guideline for the optimization of these layers in terms of their material properties; such as, Young's modulus, Poisson's ratio, and geometrical parameters. In the present study, the effects of coating layer thickness [3 nm-10 microm], Young's modulus [100 Pa to approximately 1 TPa], and Poisson's ratio [0.10 to approximately 0.45] are investigated with the finite element analysis (FEA), focusing on systems with two dimensional (2D) stress induced either on top of the coating layer (i.e., surface stress) or at the interface between the coating layer and the silicon cantilever. It is found that the coating layer can either enhance or reduce the deflection of nanomechanical sensors depending on its material properties. These results provide guidelines for designing a coating layer to achieve higher sensitivity.