Accuracy of Surface-Potential-Based Long–Wide-Channel Thick-Base MOS Transistor Models

B.B Jie,Chih-Tang Sah Chih-Tang Sah

doi:10.1109/ted.2007.900674

Abstract

This paper answers the frequently asked question, ldquoHow accurate are the approximate long-wide-channel thick-base MOS transistor baseline models that have been used to develop the compact models for computer-aided circuit designs?rdquo Three commonly used surface-potential-based( Us = qPsis / kT ) approximations of the ionized impurity bulk charge are evaluated as follows: Q B alpha (i) ( Us ) 1/2 ; (ii) ( Us -1) 1/2 ; (iii)[ Us -1 + exp(- U s )] 1/2 . The double-integral baseline model for comparison includes the self-consistent remote charge-neutrality boundary condition, minority carriers, and space-constant impurity-concentration and oxide thickness. Percentage deviations of the approximations from the baseline model are computed for the dc drain current. Approximation (i) show a significant deviation, which is ~ 16% at threshold voltage, diverging rapidly in the subthreshold range toward flatband. Approximations (ii) and (iii) show a few percent (1% to 2%) deviations in both inversion and subthreshold ranges but diverge widely below subthreshold and in accummulation. A new analytical model is tested and shows better than 10% accuracy below subthreshold and in accummulation.

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