Selector device is critical in high-density cross-point resistive switching memory arrays for suppressing the sneak leakage current path. GexSe1-x based ovonic threshold switch (OTS) selectors have recently demonstrated strong performance with high on-state current, nonlinearity and endurance. Detailed study of its reliability is still lacking and the understanding on the responsible mechanisms is limited. In this work, for the first time, the endurance degradation mechanism of Ge-rich GexSe1-x OTS is identified. Accumulation of slow defects that remain delocalized at off-state and GeSe segregation/crystallization during cycling lead to the recoverable and non-recoverable leakage current, respectively. Most importantly, a refreshing program scheme is developed to recover and prevent the OTS degradation and the endurance can be therefore improved by more than five orders without adding additional material elements or process steps.

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The over-reset phenomenon in Ta2O5 RRAM device investigated by the RTNbased defect probing technique

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Nonvolatile memories have emerged in recent years and have become a leading candidate towards replacing dynamic and static random-access memory devices. In this article, the performances of TiO 2 and TaO 2 nonvolatile memristive devices were compared and the factors that make TaO 2 memristive devices better than TiO 2 memristive devices were studied. TaO 2 memristive devices have shown better endurance performances (10 8 times more switching cycles) and faster switching speed (5 times) than TiO 2 memristive devices. Electroforming of TaO 2 memristive devices requires 4.5 times less energy than TiO 2 memristive devices of a similar size. The retention period of TaO 2 memristive devices is expected to exceed 10 years with sufficient experimental evidence. In addition to comparing device performances, this article also explains the differences in physical device structure, switching mechanism, and resistance switching performances of TiO 2 and TaO 2 memristive devices. This article summarizes the reasons that give TaO 2 memristive devices the advantage over TiO 2 memristive devices, in terms of electroformation, switching speed, and endurance.