3. How a "Real" MOS Transistor Works

The threshold voltage measured across the MOS capacitance gives us the gate voltage that separates the off and on states of an infinitely long MOS transistor. The open state corresponds to the strong inversion regime, while the off state corresponds to the other regimes. This section describes the operation of the MOS transistor, focusing on the N-type MOS transistor (nMOS), which has a P-type substrate and N-type channels, meaning that the current in the on state consists of electrons. The same reasoning can be applied to describe the operation of the pMOS, simply by changing the doping type in the equations—that is, the sign of the charges: the on-state of an nMOS is obtained when $V_{\mathrm{GS}}>0$ , whereas it is obtained...