Major challenges
concerning the reliability of resistive switching
random access memories based on the valence change mechanism (VCM)
are short-term instability and long-term retention failure of the
programmed resistance state, particularly in the high resistive state.
On the one hand, read noise limits the reliability of VCMs via comparatively
small current jumps especially when looking at the statistics of millions
of cells that are needed for industrial applications. Additionally,
shaping algorithms aiming for an enlargement of the read window are
observed to have no lasting effect. On the other hand, long-term retention
failures limiting the lifetime of the programmed resistance states
need to be overcome. The physical origin of these phenomena is still
under debate and needs to be understood much better. In this work,
we present a three-dimensional kinetic Monte Carlo simulation model
where we implemented diffusion-limiting domains to the oxide layer
of the VCM cell. We demonstrate that our model can explain both instability
and retention failure consistently by the same physical processes.
Further, we find that the random diffusion of oxygen vacancies plays
an important role regarding the reliability of VCMs and can explain
instability phenomena as the shaping failure as well as the long-term
retention failure in our model. Additionally, the results of the simulations
are compared with experimental data of read noise and retention investigations
on ZrO2-based VCM devices.
In this work, we experimentally characterize the endurance of 2 Mbit resistive switching random access memories (ReRAMs) from a 16 MBit test-chip. Here, very rare failure events where the memory cells become stuck in the low-resistive state (LRS) are observed. As this failure mechanism is the limiting one concerning the endurance of this ReRAM implementation, extensive investigations are conducted and presented. The experimental findings are detailed via a voltage divider model, illustrating why memory cells can become stuck in the LRS. It is proposed, that an insufficient voltage dropping over the cell due to an unfavorable combination of cell-and transistor resistances is responsible for stuck-at-LRS bits. Furthermore, we give predictions for the origin of these suboptimal combinations. Additionally, a onedimensional Kinetic Monte Carlo (KMC) model that allows a statistical investigation of large numbers of cells with regard to rare random events has been developed. Here, we fortify our proposed explanation for the observed failure mechanism by the simulation and evaluation of the switching process of the memory. All simulations are in very good agreement with the experimental data. Finally, based on our findings, we give suggestions for the improvement of switching algorithms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.