  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 aF range or less has been extremely difficult. Here, we report an
extraction of the capacitance down to 0.55 aF for a silicon 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 using
a classical model of current characteristics of a FET.
