The study of threshold voltage extraction of nitride spacer NMOS transistors in early stage hot carrier stress

Threshold voltage V_t extracted by g_m-maximum extrapolation method under early stage hot carrier stress is proven to be an inappropriate method once electrons are trapped in a nitride spacer. The trapping of electrons in a nitride spacer increases the series drain resistance, reducing the transconductance g_m and the corresponding gate-to-source voltage V_gs at which peak g_m occurs. It ultimately decreases the threshold voltage V_t extracted by the g_m-maximum extrapolation method. A novel algorithm is derived to determine the relationship between the measured data and the true threshold voltage of such a device under hot carrier stress by considering the effect of series resistance in g_m-maximum extrapolation method.