Random errors in MOS capacitors

Abstract

The effects of random edge variations and deviations of oxide thickness and permittivity are examined. Making only a few basic assumptions, it is shown that edge effects introduce a relative capacitance error /spl Delta/C/C/spl alpha/C/SUP -3/4/, while the oxide variations cause /spl Delta/C/C/spl alpha/C/SUP -1/2/. Error bounds are derived for C in terms of the variances of the linear dimensions and oxide permittivity. For a capacitor C realized as a parallel connection of n unit capacitors of values C/n, the relative error caused by edge effects is n/SUP 1/4/ times larger than for a single capacitor of value C. The relative error due to oxide variations remains the same for the two realizations. All theoretical results agree with physical consideration, as well as the Monte Carlo simulations performed.