Stretch-out of high-permittivity MOS capacitance–voltage curves resulting from a lateral non-uniform oxide charge distribution

This paper investigates the effect of a lateral non-uniform oxide charge distribution on the capacitance–voltage, C(V), response of a metal–oxide–semiconductor (MOS) structure. In contrast with the case of an in-depth non-uniform but laterally invariant oxide charge distribution which produces a pure voltage shift of the C(V) characteristic, we show that a lateral non-uniform charge profile can shift the curve and also stretch it under certain conditions of non-uniformity on a nanometer scale. This result is particularly important in the case of advanced MOS devices with high-permittivity gate dielectrics since such gate stacks are susceptible to present fixed charge bonding arrangements depending on the metal ion in the oxide or of the crystalline or amorphous state of the oxide. In the present study, the impact of linear, Gaussian, random and patterned oxide charge distributions are investigated for the first time using two-dimensional numerical simulations based on the solving the Poisson equation on the whole structure.