We investigated the short-term instability of HfO2-based RRAM devices during programming in the time range of 100 ns to 1 s. Our measurements demonstrate conclusively that it is fluctuation, not relaxation, that significantly degrades the effectiveness of the program-verify approach. While this new insight is valuable for understanding the problem as well as searching for a solution, we uncovered additional troubling details. We observe that the occurrence probability (frequency) of these fluctuations initially decreases (over 100 μs) before reaching a non-zero steady state value that never vanished over the time duration of our study. Even more alarming is the observation that the fluctuation amplitude never decreases within the same time duration. These observations indicate that that techniques such as delay reading or averaging will not relieve this fundamental problem .
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