50 nm Gate Length FinFET Biosensor & the Outlook for Single-Molecule Detection

We report on the smallest silicon FinFETs functioning as biosensors with 13 nm wide fins and 50 nm gate lengths. These electrolytically gated finFETs exhibit a near-ideal subthreshold swing (~65 mV/dec) and a median voltage referred 1/f noise of only ~470 μV
²
μm
²
/Hz (at 1Hz, at threshold). Binding biomolecules to the chemically modified gate dielectric surface changes the threshold voltage VT. DNA-PNA hybridization shows a statistically significant signal across all device geometries (50 nm – 10 µm gate length) with a median VT shift of 36 mV for a hybridized 15 base DNA surface density of ~8×10
¹²
cm
^-2
. We obtain a clear signal of 17 mV for a 20 base DNA surface density of ~8×10
¹¹
cm
^-2
, which amounts to tens of molecules for a 13 nm wide and 90 nm long device. This is a major improvement compared to our previously reported 250 nm long FETs which picked up ~800 molecules and a significant step forward towards the realization of single molecule sensing with fully integrated silicon FETs. Finally, based on experiment and simulation, we predict single-molecule detection with SNR > 5 to be possible with sub-70 nm finFETs.