Effect of annealing on charge transfer in Ge nanocrystal based nonvolatile memory structure

Abstract

Ge nanocrystals (nc-Ge) embedded in the gate oxide of the nonvolatile memory structure were synthesized by Ge ion implantation followed by thermal annealing at 800 °C for various durations. Large changes in the structural and chemical properties of the Ge+-implanted oxide have been observed, and they have been found to possess a significant impact on the charge transfer in the oxide layer. The distribution and concentration of the nc-Ge and dissolved Ge atoms which serve as both the charge storage and transfer sites in the oxide are affected by the annealing. Two charge transfer mechanisms, i.e., the lateral charge diffusion along the Ge-distributed layer and the charge leakage from the charge storage sites to the Si substrate via the charge transfer sites, have been identified based on the charge retention behaviors. Both mechanisms are enhanced by the annealing as a result of the change in the distribution and concentration of the charge transfer sites.