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Nafisa Noor1 Lindsay Sullivan1 5 Raihan Sayeed Khan1 Sadid Muneer1 Faruk Dirisaglik1 4 Adam Cywar1 3 Yu Zhu2 Chung Lam2 Ali Gokirmak1 Helena Silva1

1, University of Connecticut, Storrs, Connecticut, United States
5, Accenture, Dallas, Texas, United States
4, Eskisehir Osmangazi University, Eskisehir, , Turkey
3, Analog Devices, Norwood, Massachusetts, United States
2, IBM T.J. Watson Research Center, Yorktown Heights, New York, United States

Phase change memory (PCM) is an emerging non-volatile memory technology with high endurance, high speed, and good scalability. Compared to other nanoscale devices, PCM exhibits high cell-to-cell and cycle-to-cycle programming variability due to the unique amorphous and crystalline structures that form upon each reset and set operation [1]. The variability in amorphous region for cells of similar dimensions programmed to similar resistance levels can be analyzed using tunneling electron microscopy (TEM) imaging [2] but this is a difficult and time-consuming procedure. We have experimentally extracted the amorphized length of multiple PCM line cells by conducting destructive post-reset read operations with gradually increasing amplitudes until further breakdown and amorphization. The amorphized length is calculated using the reported GST breakdown field of 56 MV/m [3] and the applied voltage amplitudes at which each of the breakdowns takes place. Significant variability is observed in the measurements. For example, the amorphized lengths of 5 cells of similar dimensions (width ~130 nm, length ~470 nm, and thickness ~50 nm) amorphized at very similar resistance levels (~16-19 MΩ) vary from 32 to 55 nm. Electrical measurement results along with corresponding locations of void distributions and amorphized regions from the scanning electron microscopy (SEM) images of read disturbed cells will be presented and discussed.

References:
1. Boniardi, Mattia, et al. "Statistics of resistance drift due to structural relaxation in phase-change memory arrays." IEEE Transactions on Electron Devices 57.10 (2010): 2690-2696.
2. Santala, M. K., et al. "Distinguishing mechanisms of morphological instabilities in phase change materials during switching." Thin Solid Films 571 (2014): 39-44.
3. Krebs, Daniel, et al. "Threshold field of phase change memory materials measured using phase change bridge devices." Applied Physics Letters 95.8 (2009): 082101.

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