Quasi-static capacitance of a MOS-FET upon saturation of the carrier drift velocity

Abstract

The effect of the saturation of the carrier drift velocity on the voltage-capacitance characteristics of the gate capacitances C gs and C gd of a MOS transistor has been examined. The voltage-capacitance characteristics are studied analytically for three different approximations of the dependence of the carrier drift velocity on the field, ν(E). It is shown that the voltage-capacitance characteristic can be computed with satisfactory accuracy by means of a very simple piecewise-linear approximation. On the other hand, the voltage-capacitance characteristics must be computed on the basis of more realistic analytical dependences of ν(E), since a crude piecewise-linear approximation in this case results in serious errors. A comparison of the experimental voltage-capacitance characteristics with the theoretical results can serve as a criterion for estimating the actual law of saturation of the drift velocity.