Electrical characterization of high performance, liquid gated vertically stacked SiNW-based 3D FET biosensors

Abstract

A 3D vertically stacked silicon nanowire (SiNW) field effect transistor featuring a high density array of fully depleted channels gated by a backgate and one or two symmetrical platinum side-gates through a liquid has been electrically characterized for their implementation into a robust biosensing system. The structures have also been characterized electrically under vacuum when completely surrounded by a thick oxide layer. When fully suspended, the SiNWs may be surrounded by a conformal high-κ gate dielectric (HfO2) or silicon dioxide. The high density array of nanowires (up to 7 or 8×20 SiNWs in the vertical and horizontal direction, respectively) provides for high drive currents (1.3mA/μm, normalized to an average NW diameter of 30nm at VSG=3V, and Vd=50mV, for a standard structure with 7×10 NWs stacked) and high chances of biomolecule interaction and detection. The use of silicon on insulator substrates with a low doped device layer significantly reduces leakage currents for excellent Ion/Ioff ratios >106 of particular importance for low power applications. When the nanowires are submerged in a liquid, they feature a gate all around architecture with improved electrostatics that provides steep subthreshold slopes (SS<75mV/dec), low drain induced barrier lowering (DIBL<20mV/V) and high transconductances (gm>10μS) while allowing for the entire surface area of the nanowire to be available for biomolecule sensing. The fabricated devices have small SiNW diameters (down to dNW∼15–30nm) in order to be fully depleted and provide also high surface to volume ratios for high sensitivities.