Subthreshold parameters of radio-frequency multi-finger nanometer MOS transistors

The subthreshold radio-frequency (RF) characteristics of multi-finger nanoscale MOS transistors were studied by using the measured scattering (s) parameters. Small-signal circuit parameters were determined based on a simplified small-signal equivalent circuit model. We found that besides the source and gate resistances, most of the parameters such as the channel resistance, drain inductance and intrinsic capacitance are found to be significantly different to those in the saturation mode of operation. The subthreshold channel resistance increases and the drain inductance decreases as the finger number increases because of the more significant charge transport along the finger boundaries. In addition, the channel resistance can be governed by the drain-induced barrier lowering in a transistor with very short gate length. The equivalent intrinsic capacitance of the small-signal equivalent circuit is governed by the substrate resistance and capacitance which make the parameter extraction more difficult.