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

摘要

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 (HfO_2) 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 V_(SG)=- 3 V, and V_d= 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 I_(on)/I_(off) ratios ＞10~6 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 d_(NW)～ 15-30 nm) in order to be fully depleted and provide also high surface to volume ratios for high sensitivities.