Multi-level storage in phase-change memory: from multi-layer to single layer

ABSTRACT In this paper, we report multi-level storage (MLS) in multi-layer (ML) and single-layer (SL) phase-change memories (PCM). For the former ML-PCM device, the active medium with two layers of chalcogenide consists of a top 30-nm TiN/180-nm SbTeN/20-nm TiN/bottom 120-nm SbTeN stacked multi-layer. Three stable and distinct resistance states are demonstrated in both static and dynamic switching characteristics of the multi-layer devices. For the latter SL-PCM device, the active medium with only one layer of chalcogenide consists of a top 50-nm TiN/150-nm SbTeN. We demonstrate that the number of distinguishable resistance levels can readily reach 16 and even higher. These levels in this study result from the initial threshold switching and the subsequent current-controlled crystallization induced by Joule heating. Therefore, the latter memory allows the creation of many distinct levels, thus enabling the low-cost ultra-high-density non-volatile memory.