Robust Low Voltage Program-Erasable Cobalt-Nanocrystal Memory Capacitors with Multistacked Al₂O₃/HfO₂/Al₂O₃ Tunnel Barrier

An atomic-layer-deposited Al₂O₃/HfO₂/Al₂O₃ (A/H/A) tunnel barrier is investigated for Co nanocrystal memory capacitors. Compared to a single Al₂O₃ tunnel barrier, the A/H/A barrier can significantly increase the hysteresis window, i.e., an increase by 9V for ±12V sweep range. This is attributed to a marked decrease in the energy barriers of charge injections for the A/H/A tunnel barrier. Further, the Co-nanocrystal memory capacitor with the A/H/A tunnel barrier exhibits a memory window as large as 4.1V for 100μs program/erase at a low voltage of ±7V, which is due to fast charge injection rates, i.e., about 2.4×10¹⁶cm^-2s^-1 for electrons and 1.9×10¹⁶cm^-2s^-1 for holes.