posted on 2021-11-23, 00:43authored byNils Kopperberg, Stefan Wiefels, Sergej Liberda, Rainer Waser, Stephan Menzel
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.