Band-alignment dominated retention behaviors in high-k composite charge-trapping memory devices

A nonvolatile memory structure with a high-k composite of ZnO-TiO2 as a charge-trapping dielectric was fabricated by using rf-sputtering and atomic layer deposition techniques, in which the potential of the conduction-band minimum of the composite was designed to be lower than that of Si by the use of the special energy-band offsets among Si, ZnO, and TiO2. Compared to the conduction-band minimum of Si, a relatively negative potential of the high-k composite leads to a continuous rise in the shift of the flat-band potential of the memory device except a drop at the beginning part of the time-dependent retention curve after a programming operation. The drop was attributed to the escape of trapped charges at the Si/Al2O3 interface. After extracting the contribution to the deterioration of the retention curve from the traps at the Si/Al2O3 interface, it was identified that the band alignment in a charge-trapping memory device dominated its retention behaviors.