UNIVERSALITY OF ELECTRON-MOBILITY CURVES IN MOSFETS - A MONTE-CARLO STUDY

The universal behavior of electron mobility when plotted versus the effective field is physically studied. Due to charged centers in the silicon bulk, the oxide, and the interface, Coulomb scattering is shown to be responsible for the deviation of mobility curves. Silicon bulk-impurities have a double effect: (a) Coulomb scattering due to the charge of these impurities themselves, and (b) reduction of screening caused by the loss of inversion charge,when the depletion charge is increased. The electric-field region in which mobility curves behave universally regardless of bulk-impurity concentration, substrate bias, or interface charge has been determined for state-of-the-art MOS-FETs. finally, this study shows that electron mobility must be a function of the inversion and the depletion charges rather than a simple function of the effective field.