Size independent sensitivity to biomolecular surface density using nanoscale CMOS technology transistors

We investigate the impact of field effect transistor (FET) transducer size on its sensitivity to biomolecular surface charge density, as would be encountered in a bulk biomolecule concentration measurement. We characterize electrolytically gated transistor sensors fabricated completely using CMOS FinFET technology and analyse a wide range of channel lengths (3000 nm to 450 nm) and widths (1000 nm to 60 nm). We measure saturated density of biomolecules on the transducer surface in order to eliminate variabilities related to association kinetics or affinity effects of the analyte-receptor biomolecules. We use transistor gate voltage shift to quantify the saturated PNA/DNA hybridization signal. We observe no significant dependence of saturated DNA hybridization signal (29.5 ± 3.7 mV) on transistor dimensions for 15 base pair long DNA with an areal density of about $8.3\times 10^{4}$ DNA/ $\mu \text{m}^{2}$ measured in 1.5 mM buffer. We also confirm these experimental findings by 3D TCAD simulations for transistor widths down to 10 nm, with less than 6% variation in voltage transduction sensitivity versus width. TCAD analysis was also performed for scaling of the FET height from 250 nm down to 5 nm, resulting in a similar small drop in voltage transduction sensitivity (~ 5.5% for a 250 nm wide FET and ~ 14.6% for a 10 nm wide FET). These results show that the FET sensor downscaling does not significantly improve or degrade voltage transduction sensitivity to a charge (or molecule) density.