Stacked HfAlO-SiO2 tunnel layers are designed for Pd nanocrystal nonvolatile memories. For the sample with 1.5 nm-HfAlO/3.5 nm-SiO2 tunnel layer, a smaller initial memory window is obtained compared to the sample with 3.5 nm-HfAlO/1.5 nm-SiO2 tunnel layer. Owing to the thermally induced traps in HfAlO-SiO2 films are located at a farther distance from the Si substrate and more effective blocking of charge leakage by asymmetric tunnel barrier, a larger final memory window and better retention characteristic can be obtained for Al/blocking oxide SiO2/Pd NC5/1.5 nm-HfAlO/3.5 nm-SiO2/Si structure. A N-2 plasma treatment can further improve the memory characteristics. Better memory characteristics can be obtained for Pd-nanocrystal-based nonvolatile memory with an adequate thickness ratio of HfAlO to SiO2. (C) 2011 Elsevier Ltd. All rights reserved.