Charging and discharging characteristics of metal nanocrystals in degraded dielectric stacks

The conduction mechanisms of dielectric breakdown (BD) in MOS capacitor structure with nanocrystals (NCs) embedded in bi-layer gate stacks (SiO₂/Al₂O₃) are studied systematically. Using a unique stressing methodology of inducing a BD path in one dielectric layer, the charging and discharging phenomenon of the metal NCs and leakage mechanism in the degraded gate stacks are found to be strongly dependent on the lateral charge tunneling/hopping among the NCs. It is found that the localized BD not only affects charge holding capability of the affected NCs, but also provides a leakage path for the charges stored in the surrounding NCs. Thus, the discharging of NCs via the BD path is not a localized phenomenon.