Analysis of the channel inversion layer capacitance in the very thin-gate IGFET

As the gate insulator thickness approaches the channel thickness, the gate capacitance is speculated to be smaller than its gate insulator capacitance. The gate capacitance of the thin-gate IGFET is calculated using Maxwell-Boltzmann and Fermi-Dirac statistics and is experimentally measured. The results show that the gate capacitance approaches the gate insulator capacitance regardless of the gate thickness within the practical range (T_{ox} > 50Å). To explain why the channel thickness is not reflected in the measured gate capacitance, the channel inversion layer capacitance is analyzed numerically. Based on that, its effects on the gate capacitance are discussed quantitatively and an equivalent circuit is proposed.