Accuracy of Surface-Potential-Based Long-Wide-Channel MOS Transistor Compact Models

摘要

This paper answers the frequently asked question, "How accurate are the approximate baseline long-and-wide-channel MOS transistor models that have been used to develop the compact models for computer-aided circuit designs?" Three commonly used surface-potential-basedrn(U_S=qψ_S/kT) approximations of the bulk-charge arernevaluated: Q_B ∝ (ⅰ) (U_S)~(1/2), (ⅱ) (U_S-1)~(1/2), and (ⅲ) [U_S-1+exp(-U_S)]~(1/2). Self-consistent remote charge neutrality boundary condition, minority carriers, and space constant impurity concentration and oxide thickness are used. Percentage deviations of the approximations from the non-compact baseline model are computed for DC drain current, drain- and trans-conductances. Approximation (ⅰ) shows significant devia-tions, ～16% at threshold diverging rapidly with deepening into the subthreshold range. Approximations (ⅱ) and (ⅲ) show a few percent (1% to 2%) deviations in both inversion and subthreshold ranges, but diverge widely below sub-threshold and in accumulation. A new analytical model is tested and shows better than 10% accuracy in accumulation.