Role of velocity saturation in lifting pinchoff condition in long-channel MOSFET

The role of velocity saturation due to high-field mobility degradation in lifting the pinchoff condition in a long-channel MOSFET is described. The electric field on the drain end at the onset of current saturation is always extremely high leading to the velocity saturation of the carriers. This velocity saturation leads to the saturation value n_sD=n_soV_g´/2V_c=I_Dsat/q nu _th W on the drain end, in contrast with the well-known pinchoff behaviour, where the carrier density is shown to vanish at the saturation point. The carrier distribution, as well as the velocity distribution as a function of the channel distance along the length of the channel, is presented.