Resistance Drift and Crystallization in Suspended and On-oxide Phase Change Memory Line Cells

Abstract

Resistance drift and crystallization are critical concerns for accurate distinction between different states and for data retention in phase change memory (PCM), but their underlying physical mechanisms are still not fully understood. In this work, we compared the resistance drift and crystallization of suspended and on-oxide amorphous Ge2Sb2Te5 PCM line cells. We programmed 15 cells of each type at room temperature to a resistance level of ~10 MΩ and monitored their resistance over ~3 months. The initial upward resistance drift trends were very similar for both cell types, but the later behaviour was noticeably different. The suspended cells exhibited increased variability in the upward drift after ~103 s, and at ~35-80 days some cells experienced an abrupt crystallization, some showed a saturation in the upward resistance drift, and others continued the upward resistance drift with fluctuations, possibly due to the imminent saturation. The on-oxide cells, on the other hand, demonstrated very consistent upward resistance drift during the entire measurement period. Temperature-accelerated measurements at 400 K on both type of cells also showed the early and abrupt data loss in suspended cells. The abrupt crystallization in suspended PCM cells can potentially be useful for self-destructive hardware security primitives based on the loss of the stored data after a certain time.