Investigation of the dominant 1/f noise source in silicon nanowire sensors

We analyzed 1/f noise in silicon nanowire ion-sensitive field-effect transistors (SiNW-ISFETs) having different wire widths ranging from 100 nm to 1 μm and operated under different gating conditions in order to determine the noise source and the sensor accuracy. We find that the gate-referred voltage noise SVG (power spectral density) is constant over a large range of SiNWs resistances tuned by a DC gate voltage. The measurements of SVG for SiNWs with two different gate-oxide thicknesses, but otherwise similar device parameters, are only compatible with the so-called trap state noise model in which the source of 1/f noise is due to trap states residing in the gate oxide (most likely in the interface between the semiconductor and the oxide). SVG is found to be inversely proportional to the wire width for constant wire length. From the noise data we determine a sensor accuracy of 0.017% of a full Nernstian shift of 60 mV/pH for a SiNW wire with a width of 1 μm. No influence of the ions in the buffer solution was found.