Evaluation of a Gate Capacitance in the Sub-aF Range for a Chemical Field-Effect Transistor With a Si Nanowire Channel

An evaluation of the gate capacitance of a field-effect transitor (FET), whose channel length and width are several ten nanometer, is a key point for sensors applications. However, experimental and precise evaluation of capacitance in the attofarad range or less has been extremely difficult. Here, we report an extraction of the capacitance down to 0.55 aF for a Si FET with a nanoscale wire channel, whose width and length are 15 and 50 nm, respectively. The extraction can be achieved by using a combination of four kinds of measurements: current characteristics modulated by double gates, random-telegraph-signal noise induced by trapping and detrapping of a single electron, dielectric polarization noise, and current characteristics showing Coulomb blockade at low temperature. The extraction of such a small gate capacitance enables us to evaluate electron mobility in a nanoscale wire by using a classical model of current characteristics of an FET.