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

The universal behavior of electron mobility when plotted versus the ef fective field is physically studied. Due to charged centers in the sil icon bulk, the oxide, and the interface, Coulomb scattering is shown t o be responsible for the deviation of mobility curves. Silicon bulk-im purities have a double effect: (a) Coulomb scattering due to the charg e of these impurities themselves, and (b) reduction of screening cause d by the loss of inversion charge,when the depletion charge is increas ed. The electric-field region in which mobility curves behave universa lly regardless of bulk-impurity concentration, substrate bias, or inte rface charge has been determined for state-of-the-art MOS-FETs. finall y, this study shows that electron mobility must be a function of the i nversion and the depletion charges rather than a simple function of th e effective field.