Effects of traps on charge storage characteristics in metal-oxide-semiconductor memory structures based on silicon nanocrystals

Charge storage characteristics have been investigated in metal-oxide-semiconductor memory structures based on silicon nanocrystals, where various interface traps and defects were introduced by thermal annealing treatment. The observations demonstrate that traps have strong influence on the charge storage behavior, in which the traps and defects at the internal/surface of silicon nanocrystals and the interface states at the SiO2/Si substrate play different roles, respectively. It is suggested that the injected charges are mainly stored at the deep traps of nanocrystals instead of the conduction band in long-term retention mode. The long-term charge-loss process is dominantly determined by the direct tunneling of the trapped charges to the interface states in the present experiment. An optimum way to improve the retention time would be to introduce a certain number of deep trapping centers in nanocrystals and to decrease the interface states at SiO2/Si substrate.