Off-state mode TDDB reliability for ultra-thin gate oxides: New methodology and the impact of oxide thickness scaling

A simple and practical new methodology, a so-called voltage-splitting technique, is proposed for reliability evaluation of the off-state mode in ultra-thin gate oxides. By applying a negative voltage on the gate while the drain is biased at the operational voltage, we successfully resolve the difficulty associated with the unrealistic high drain-bias stress, which leads to the excessive damage to oxides in the overlap region. Using this technique, we have demonstrated that the normalized breakdown results of the off-state mode are compatible with those obtained in the inversion mode with proper account for edge-tunneling current and effective area. The impact of high drain-bias stress has been shown to be detrimental to oxide integrity due to the presence of additional degradation mechanisms. Our results indicate that off-state oxide reliability will become an increasingly important concern as oxide thickness is scaled down.