Prototypical lateral multi-state phase-change memory with a multi-layer medium

In this paper, we propose a lateral multi-state phase-change memory based on low-power crystallization (especially, initial filament formation induced by electric field) process. The active medium in the fabricated devices is an N-doped Sb₂Te₃ (STN) based multi-layer, that is, a top 30-nm TiN/180-nm STN/20-nm TiN/bottom 120-nm STN stacked structure. Three stable and distinct resistance states are demonstrated in both static and dynamic switching characteristics of the multi-layer devices. Analysis reveals that two separate crystallization processes causing the two resistance drops could sequentially occur at the steps from the bottom thin 120-nm STN layer to the top thick 180-nm STN layer due to the electric field confinement at the steps.