Thickness dependence of Al2O3/HfO2/Al2O3 stacked tunneling layers on gadolinium oxide nanocrystal nonvolatile memory

•Study of Gd2O3-NC memories with Al2O3/HfO2/Al2O3 (AHA) stacked tunnelling layers.•Superior P/E properties achieved by Gd2O3-NC memories with optimized AHA layers.•Improved retention properties obtained by Gd2O3-NC memories with AHA layers.•Gd2O3-NC memories with stable VFB after a P/E cycling test of 104 times realized.

Characteristics of Gd2O3-NC memories with multiple tunneling layers of Al2O3/HfO2/Al2O3 (AHA) have been investigated. It can be found that the Gd2O3-NC memory with thin bottom and thin top Al2O3 film of AHA stacked tunneling layers exhibits superior programming and erasing (P/E) properties, respectively. Compared with the memory with SiO2 tunneling layer, the retention characteristics of Gd2O3-NC memories with AHA stacked tunneling layers are significantly improved. In addition, for the memories with AHA stacked tunneling layers, the trapping energy level (Et) of shallow-trap (ST) electron loss is decreased but that of deep-trap (DT) electron loss is increased due to some shallow traps within HfO2 film and the midgap interface states at HfO2/Si interface respectively. Further, the dependence of AHA stacked layer thickness on memory characteristics can be explained by the band engineering of tunneling layer. The Gd2O3-NC memories with AHA stacked tunneling layers can sustain a stable memory window of more than 1.6 V after a P/E cycling test of 104 times.

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