Intrinsic program instability in HfO2 RRAM and consequences on program algorithms

We statistically investigated for the first time resistance stability in HfO₂ RRAM devices in the short (μs to s) transient after switching. We show that, the resistance value of both logic states is not stable after programming and subject to large discrete stochastic fluctuations. The frequency of fluctuation is found to be time-decaying thus hindering its detection in DC condition but considerably affecting throughput and effectiveness of write algorithms. We finally identify this instability as the primary source of the well-known resistance variability and we qualitatively explain it in terms of relaxation oscillation of filament microscopic configuration.