In this paper, we describe the effects that five metallic contaminants have on the electrical property of an ultrathin gate oxide. We found that, among five metallic contaminants, Fe and Ni resulted in the lowest electric breakdown fields (E-bd) and charge-to-breakdown ratios (Q(bd)) and the highest leakage currents and interface state densities (D-it). On the other hand, Ca-contaminated devices exhibit a lower leakage current and D-it and a higher Q(bd) than did the other metals. (c) 2005 The Electrochemical Society.