Hole and electron trapping in HfO₂/Al₂O₃ nanolaminated stacks for emerging non-volatile flash memories

HfO₂/Al₂O₃ 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 Al₂O₃ thickness and post-deposition oxygen annealing. Depending on the Al₂O₃ thickness, post-deposition annealing in O₂ creates different electrically active defects (oxide charge and traps) in the stacks. O₂ 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 × 10⁴ program/erase cycles.