A three-dimensional MOSFET solver implementing the fixed point iteration technique

Our implementation of a fixed-point iteration technique for the three-dimensional (3D) steady-state simulation of MOSFET devices is presented. The simulation program is employed to investigate narrow channel effects on the device current-voltage characteristics. Particularly, the effects of impact ionization and the effects of variations in channel width and the field oxide bird's beak angle are evaluated. The degree to which various field oxide configurations isolate the device from the gate contact over the oxide transition region is determined by comparing the current-voltage characteristics with those of an idealized device with perfect isolation. Perfect isolation is simulated by setting the normal component of the electric field to zero at the semiconductor-field oxide interface. Simulation results show that the 3D computations are essential to account for rapidly varying charge densities and generation rates near the channel edge. Moreover, it is observed that the isolation effects of field oxides increase for larger bird's beak angles.