Hole and electron trapping in HfO_2/Al_2O_3 nanolaminated stacks for emerging nonvolatile flash memories

摘要

HfO_2/Al_2O_3 nanolaminated stacks prepared by atomic layer deposition have been investigated in terms of their charge storage characteristics for possible application in charge trapping memories. It is shown that the memory window, electron and hole trapping and leakage currents depend strongly on Al_2O_3 thickness and post-deposition oxygen annealing. Depending on the Al_2O_3 thickness, postdeposition annealing in O_2 creates different electrically active defects (oxide charge and traps) in the stacks. O_2 annealing increases electron trapping, thus giving rise to a larger memory window and enhanced charge storage characteristics, i.e. 65% of charge is retained after ten years and the memory window decreases by 6% after 2.5×10~4 program/erase cycles.