DNA detection with top-down fabricated silicon nanowire transistor arrays in linear operation regime

Abstract

Silicon nanowire field-effect transistors (SiNW-FETs) are offering a label-free sensing of DNA molecules based on the detection of the biomolecules' charges. Typically, the charge accumulation at the solid-liquid interface is leading to a change in surface potential of the device. In other works, this effect is usually displayed as change in conductance of the nanowires. In this paper, we show that our topdown processed SiNW-FET devices can be regarded as long-channel, ion-sensitive field-effect transistor devices (ISFETs) and that their electronic characteristics can be fitted by an advanced MOSFET model taking narrow channel effects into account. In DNA experiments, changes in threshold voltage upon immobilization of capture DNA and hybridization with complementary target DNA were recorded as reported before. The signal amplitudes were scaling with different concentrations of electrolyte buffer as known from the commonly used Poisson-Boltzmann theory. In reports from other groups, the sensitivity of SiNW-FETs was reported to be superior compared to ISFETs and scaling effects were observed with smaller wires having higher sensitivities. From our experiments, it seems that the immobilization of the DNA to the wire structure is leading to two effects: firstly, the threshold voltage is changing, leading to a shift in the transistors' transfer characteristics similar to what was described for ISFET devices. In addition, upon DNA binding, a general increase in charge carrier density inside the nanowire is leading to an enhanced conductance. We assume that the latter effect is scaling with nanowire dimensions, while the surface effect is typically constant for all sensor structures.