The need for an explicit model describing MOS transistors in moderate inversion

Explicit expressions are derived for the drift and diffusion components of the channel current as a function of position along the channel of a MOSFET. It is shown that in moderate inversion the assumption that the channel current is `mostly due to diffusion¿ or `mostly due to drift¿ can lead to not only quantitative but also qualitative errors, since drift and diffusion can dominate simultaneously, but at different parts of the channel.