Selective surface functionalization of Si and poly-SiGe resonators for a monolithic integration of bio- and gas sensors with CMOS

Resonant SOI-CMOSFET NEMS gas/bio sensors represent an important fundamental research topic and an emerging technology for many applications, thanks to the high flexibility offered by the surface functionalization methods which can tailor sensing layers for a large variety of gases and biomolecules. Self-assembled monolayers (SAMs) are one of the most relevant functionalization approaches to achieve selectivity in the sensing processes. Although the optimization of these organic films has received considerable attention, most of the functionalization routes have focused on the coating of sensors with relative large areas. The downscaling of the SAMs to small nano-devices, such as Si and poly SiGe NEMS and MEMS-based sensors, requires additional tools, both for their selective deposition and characterization. In this work, two main approaches to selective Si nanowires functionalization are being investigated: i) selective Joule heating ablation of the protective polymer layer on the suspended NW surface, and ii) e-beam lithography to open the resist layer on the NW area. In a following step, a NH2-SAM layer is deposited on the unprotected silicon oxide surface and glutaraldehyde molecules are used as a linker between the SAM amino functionality and biotin. The frequency shift response during CO2 sensing is studied as a function of an increasing number of amino functionalities of the silanization precursors. Finally Kelvin probe atomic force microscopy allows mapping the functionalized area due to the observed shift in surface potential between bare and SAMs-coated SiO2 surface.