Surface Charge Sensitivity of Silicon\nNanowires:  Size Dependence

Abstract

Silicon nanowires of different widths were fabricated in silicon on insulator (SOI) material using conventional process technology combined\nwith electron-beam lithography. The aim was to analyze the size dependence of the sensitivity of such nanowires for biomolecule detection\nand for other sensor applications. Results from electrical characterization of the nanowires show a threshold voltage increasing with decreasing\nwidth. When immersed in an acidic buffer solution, smaller nanowires exhibit large conductance changes while larger wires remain unaffected.\nThis behavior is also reflected in detected threshold shifts between buffer solutions of different pH, and we find that nanowires of width >150\nnm are virtually insensitive to the buffer pH. The increased sensitivity for smaller sizes is ascribed to the larger surface/volume ratio for\nsmaller wires exposing the channel to a more effective control by the local environment, similar to a surrounded gate transistor structure.\nComputer simulations confirm this behavior and show that sensing can be extended even down to the single charge level.