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 (1.3 mA/μm, normalized to an average NW diameter of 30 nm at VSG = 3 V, and Vd = 50 mV, 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 < 75 mV/dec), low drain induced barrier lowering (DIBL < 20 mV/V) and high transconductances (gm > 10 μS) 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 ∼ 15–30 nm) in order to be fully depleted and provide also high surface to volume ratios for high sensitivities.