Impact of tunnel currents and channel resistance on the characterization of channel inversion layer charge and polysilicon-gate depletion of sub-20-Å gate oxide MOSFET's

This paper discusses the limitations on MOSFET test structures used in extracting the polysilicon gate doping from capacitance-voltage (C-V) analysis in strong inversion, especially for ultrathin gate oxides. It is shown that for sub-20-Angstrom oxide MOS devices, transistors with channel lengths less than about 10 mu m will be needed to avoid an extrinsic capacitance roll-off in strong inversion. The upper limit of the channel length has been estimated using a new simple transmission-line-model of the terminal capacitance, which accounts for the nonnegligible gate tunneling current and finite channel resistance.